Here's my worthless views...
As we know in Mahayana, generally Boddhisattva is classified into 10 level.
True but 'Bodhisattva' can also mean those who are first aspiring in this Path, the category you mentioned and also accomplished past Buddhas who manifest/emanate the form of a Bodhisattva in order to fulfill their past vows for the sake of liberating sentient beings.
If we look Boddhisattva Avalokiteshvara, it is clear that on top of his head he received a blessing from Amitabha Buddha. Therefore, we cannot classified Avalokiteshvara as a Buddha. Otherwise, it doesn't make sense to think Buddha blessing Buddha.
Firstly, a future Samyak Sambuddha receives a prediction of Samyak Sambuddhahood from a present Buddha.
Similarly, Avalokitesvara received his prediction of from Amitabha Buddha, who is his own teacher, like how Sakyamuni in a former life received from the past Buddha, Dipamkara and Maitreya, being the designated fifth Buddha from the present Sakyamuni Buddha, who is the fourth Buddha in this Fortunate Aeon.
In some teachings I have heard, in the 11 faces/head of Avalokitesvara, the top face/head, which is a Buddha face/head, has a 2 fold explanation.
The first is the head/face is that of Amitabha Buddha, who is Avalokitesvara's teacher, who has also vowed to lead and promote the Dharma Door of the Western Pure Land of Amitabha Buddha, that's why in the Threefold Pure Land Sutras, you can read about His presence and role there. The second is that it represents the ability of Avalokitesvara of emanating a Buddha form to bridge the Dharma across to those who need this form for Liberation.
Now, Avalokitesvara Bodhisattva Himself is a past Buddha who is now manifesting an appearance of a Bodhisattva and the famous Great Compassion Mantra (which is recited all over the East Asian Buddhist world) is the one that propelled His level of attainment which was taught to Him by another past Buddha, the Thousand Rays King Stillness Thus Come One as one can read in this Sutra
Avalokitesvara Bodhisattva then said to the Buddha:
"Bhagavan, I remember that countless billions of kalpas ago, a Buddha, whose name was Thousand Rays King Stillness Thus Come One, appeared in the world. Because of his mercy and mindfulness towards me and all living beings, that Buddha, the World Honored One spoke this Vast, Perfect, Unimpeded, Great Compassionate Heart Dharani, rubbed my crown with His golden hand and said:
'Virtuous man, you should hold this heart-mantra to give great benefit and happiness to all living beings in the future evil age.'
At that time I was just at the first Bhumi (stage of Bodhisattva), right after hearing this Mantra, I exceeded the eighth Bhumi.
At that time, as my heart was joyful, I vowed:
'If I will be able to give benefit and happiness to all living beings in the future, let me have one thousand hands and one thousand eyes immediately.' Instantly after the vow, I got fully one thousand hands and one thousand eyes on my body, then, the grounds of the worlds of the ten directions quaked in six ways, thousands of Buddhas of the ten directions emitted their light to my body and illuminated boundless worlds of the ten directions.
From then on, from countless Buddhas and congregations, I have repeatedly heard, accepted and held this Dharani, and the joys were also repeatedly aroused from My heart, and made Me greatly enthusiastic. Therefore, I transcended imperceptible births and deaths of countless billions of kalpas. Since then, I have always been reciting and holding this Mantra, and have never forgotten it.
Because of holding this Mantra, I was always born by miraculous creation (nirmana) from lotuses in front of Buddhas, and have never been born from any womb."
He mentions His teacher, Amitabha Buddha...
"After making these vows, recite My Name (Namo Avalokitesvara Bodhisattva) with the deep-felt sincere heart, also recite single-mindedly the name of My Teacher -- Amitabha Tathagata (Namo Amitabha), then recite this Mantra, 5 times or more in a day, to remove from the body the weighty sins of births and deaths accumulated in hundreds of thousands of billions of kalpas."
And on His attainment of Buddhahood....
Then Ananda asked the Buddha:
"Bhagavan, what is the name of this Bodhisattva-Mahasattva, who is so good to teach us this Dharani?"
The Buddha said:
"This Bodhisattva is called Avalokitesvara, the Unrestricted One, also called Nipping a Lariat, also called A Thousand Bright Eyes.
Virtuous man, this Avalokitesvara Bodhisattva has unimaginable mighty and holy powers.
Uncountable kalpas before, He had already been a Buddha named True Dharma Brightness Tathagata.
Because of the power of His Great Compassionate Vows, and in order to call upon all Bodhisattvas to comfort and please all living beings, He appears as a Bodhisattva.
All of you, including the Bodhisattvas, Brahmas, Gods of the 33 heavens, dragons, and divinities, should show respect to Him, do not despise Him. All heavenly and human beings should constantly make offerings to Him and recite His name absorbedly, then they will get infinite blessings and eliminate countless sins, and at the end of their lives, they will be reborn in the Pure Land of Amitabha Buddha."
And His emanations...
From the Chapter 25, Wonderful Dharma Lotus Flower Sutra:
Inexhaustible Intention Bodhisattva said to the Buddha,
"World Honored One, how does Guanshiyin Bodhisattva roam through this Saha world? How does he speak the Dharma for living beings?
How does he carry out this work with the power of expedients?"
The Buddha told Inexhaustible Intention Bodhisattva,
"Good man, if living beings in this land must be saved by means of someone in the body of a Buddha...Pratyekabuddha...Hearer...Brahma King...
Shakra...God of Sovereignty...Great God of Sovereignty...a great heavenly general...Vaishravana...a minor king...an Elder...a layman...a minister of state...a Brahman...a Bhikshu, Bhikshuni, Upasaka, or Upasika....the body of the wife of an Elder, of a layman, of a minister of state, or of a Brahman...the body of a pure youth or a pure maiden...the body of a heavenly dragon, yaksha, gandharva, asura, garuda, kinnara, mahoraga, human, or nonhuman, and so forth...the body of a Vajra-wielding spirit....Guanshiyin Bodhisattva will manifest the body of a Buddha ... Pratyekabuddha ... Hearer...Brahma King...Shakra...God of Sovereignty...Great God of Sovereignty...a great heavenly general...Vaishravana...a minor king...an Elder...a layman...a minister of state...a Brahman...a Bhikshu, Bhikshuni, Upasaka, or Upasika....a wife's body...in such a body...the body of a Vajra-wielding spirit and speak Dharma for them.
"Inexhaustible Intention! Guanshiyin Bodhisattva has accomplished merit and virtue such as this and, in all manner of forms, roams throughout the land, saving and liberating living beings.
"Inexhaustible Intention, such is the self-mastery and spiritual power of Guanshiyin Bodhisattva, who roams throughout the Saha World."
Complete with the power of spiritual penetrations,
Vastly cultivating wisdom and expedient means,
Going throughout countries in the ten directions,
He manifests everywhere in all places.
The question is to Siddharta Gautama. Some people mention that Siddharta Gautama is already a Buddha before he came to earth. In your opinion, is this true?Or do you think that Siddharta Gautama is a Boddhisattva before he came to earth, where he reach his Buddha on earth through his difficult journey?
Again, this is from Chapter 16, The Wonderful Dharma Lotus Flower Sutra...
At that time the Buddha spoke to the great hosts of Bodhisattvas, saying,
"Good men, I shall now explain this clearly for you. If all these world systems whether a dust mote was deposited in them or not were reduced to dust motes, and if each dust mote were an eon, the time that has passed since I became a Buddha would exceed even that by hundreds of thousands of myriads of kotis of nayutas of asamkhyeyas of eons.
"From that time on, I have always remained in the Saha World, speaking the Dharma to teach and transform beings. Also, in other places, in hundreds of thousands of myriads of kotis of nayutas of asamkhyeyas of lands, I have guided and benefited living beings.
"Good men, in that interval, I spoke of the Buddha Dipankara and others, and I further spoke of them as entering Nirvana, but those were just discriminations made expediently.
"Good men, if a living being comes before me, I observe with my Buddha eye his faith and other qualities, as well as the keenness or dullness of his faculties, and I take him across in an appropriate manner.
"In all places, although the names by which I refer to myself are different and I may be older or younger, I also appear and announce that I am about to enter Nirvana. I also employ various expedient devices, speaking the subtle and wonderful Dharma and enabling living beings to bring forth happiness in their minds.
"Good men, the Thus Come One, seeing living beings delighting in lesser dharmas, beings of scanty virtue and heavy defilements, speaks for these people, saying, 'When young, I left the home-life and attained anuttara samyak sambodhi.'
In truth, however, I became a Buddha a long time before that. I speak in this way merely as an expedient to teach and transform living beings and to cause them to enter the Buddha Way.
"Good men, the Sutras proclaimed by the Thus Come One are all for the purpose of saving and liberating living beings. He may speak of his own body, or he may speak of someone else's body. He may manifest in his own body, or he may manifest in someone else's body. He may manifest his own affairs, or he may manifest the affairs of others, but all that he says is true and not false.
"What is the reason for this? The Thus Come One knows and sees the triple realm as it really is. There is no birth or death, no retreating or advancing, no existence in the world or passage into quiescence. There is no reality or unreality, no likenesses or differences. He views the triple realm as not being the triple realm. Matters such as these, the Thus Come One clearly sees, without mistake or error.
"Living beings have various natures, various desires, various modes of conduct, and various ideas, thoughts, and discriminations. Wishing to lead them to produce the roots of goodness, he employs divers causes and conditions, analogies, and expressions to explain the various dharmas, carrying out the Buddha's work without respite.
"Thus since I realized Buddhahood in the very remote past, my life span has been limitless asamkhyeyas of eons, eternal and never extinguished. Good men, the life span I realized when formerly practicing the Bodhisattva path has not yet been exhausted and is twice that of the above number.
"As I now proclaim that I am about to enter quiescence, I am not really passing into quiescence. The Thus Come One uses this passing only as an expedient to teach and transform living beings.
"For what reason? If the Buddha were to stay in the world a long time, those of scanty virtue who do not plant good roots, who are poor and lowly, who covet the objects of the five desires, and who are caught in the net of schemes and false views, seeing the Thus Come One constantly present and not entering stillness, would become arrogant, lax, and indifferent. They would not consider how difficult it is to encounter him, nor would their hearts be reverent.
If you want further elaboration on this matter, I can think of 3 options:
a. Google sources or look for a Nichiren priest on commentaries from Nichiren interpretation as this Sutra is their main practice
b. You can raise a question on this in the Tendai Forum and we are fortunate to have Jikan, our Global Moderator here, an ordained priest in the Tendai Tradition which also upholds the Lotus Sutra.
c. Anyone else learned enough to comment on the Lotus Sutra and from other Dharmic perspectives.
Now, there is also a similar feat like the above by Avalokitesvara Bodhisattva in the Western Pure Land and later by the third Sage of the Western Pure Land, Mahastamaprapta Bodhsattva...in this Sutra
The Buddha said, “Good man, although Amitābha Buddha’s lifespan will last innumerable hundreds, thousands, and koṭis of kalpas, it will finally come to an end. Good man, after incalculable distant kalpas to come, Amitābha Buddha will enter parinirvāṇa. After His Parinirvāṇa, the true Dharma will continue for as long as His lifespan. The number of sentient beings that will be delivered will equal that during His life.
After Amitābha’s Parinirvāṇa, some sentient beings there will not be able to see a Buddha. However, Bodhisattvas who have attained the Thinking-of-Buddhas Samādhi will constantly see Amitābha Buddha. Furthermore, good man, after His Parinirvāṇa, all the precious things, such as bathing ponds, lotus flowers, and jeweled trees in lines, will continue to sound Dharma tones, in the same way as during that Buddha’s life.
“Good man, [the night] Amitābha Buddha’s true Dharma ends, after the midnight period, when the dawn breaks, Avalokiteśvara Bodhisattva, seated cross-legged under the bodhi tree made of the seven treasures, will attain anuttara-samyak-saṁbodhi.
He will be called Universal Radiance Virtue Mountain King, the Tathāgata, Arhat, Samyak-Saṁbuddha, Knowledge and Action Perfected, Sugata, Understanding the World, Unsurpassed One, Tamer of Men, Teacher to Gods and Humans, Buddha the World-Honored One. His Buddha Land will be naturally made of the seven treasures. Even in kalpas as numerous as the sands of the Ganges, Buddha-Bhagavāns will not be able to finish describing its splendors."