In Mahayana, there are 10 Bhumis, or stages to Buddhahood. Here is the list:
*10 Bhumis to Buddhahood. [Sanskrit/Pali for plane, storey or level].
The realization of Emptiness, shunyata, is the goal. Therefore, the bhumis are the consequences of virtue-in-action. The bhumis are also interpreted as reflecting the 3 kayas or levels of "reality."
Two sutras which discuss the bhumis: Dasabhumi (Sutra of Ten Bhumis) and Samadhi-nirmochana (Explaining Profound Secrets.)
Chandrakirti, in the Bodhisattva-Avatara Shastra explains:
0. The Foundation: Beings in samsara [the 6 realms] having generated the aspiration to climb the Bodhisattva Bhumis by practicing the 6 paramitas.
Now we proceed through 3 stages on the Path of Accumulation and 3 more stages on the Path of Unification:
1. "The Joyous": Having tasted shunyata [emptiness], we are joyous. Here, the main practice is to perfect the Generosity Paramita. You might be born as a King in the Human Realm and have lots of chances to practice generosity! Now on the Path of Seeing, we can start the Path of Meditation.
2. "The Stainless": At this bhumi, the main practice is the perfection of Shila [discipline of vows] because of which you are free of anxiety and the 3 Poisons [negative tendencies, obscurations]. You might be born as a chakravartin (King bearing the noble marks of an emperor, like Siddartha Gautama Shakya), whose power and enjoyment are challenged by the practice of discipline and precept-keeping.
3. "The Luminous": Here, we try to perfect Patience or equanimity. This is the source of the luminosity. You might be born as Indra, King of gods, who is called Shakra, -- opposer of the Ashuras.
4. "The Radiant": After the 3rd Bhumi, the Nirmanakaya aspect of Buddhahood has been perfected. But there are two more Kayas, therefore, the Paramita to perfect here is that of Exertion. This activity in the service of virtue creates a radiance of wisdom which burns away false conceptions. Here, you might be reborn as Shyama, a deity in the "Continuous Peaceful Realm").
5. "The Unconquerable": Driven by exertion, you perfect
dhyana [meditation] and other skillful means in preparation for the helping of all sentient beings. The word unconquerable refers to both the difficulty of achieving the state of dhyani and the state of the being having now achieved this goal. Now it is possible to be born as a god in the Tushita Heavens where you can observe the Six Realms and the interplay of dharmas.
6. "The Manifest": The intense practice of dhyana and other skills enables you to be reborn as a God-king who can manifest miraculous activity. The Paramita of Prajna is to be perfected.
7. "The Gone-Afar": Having perfected the Six Paramitas, we now possess both wisdom and skill. This is a plateau below which you will not fall, but there is still room for effort.
In the 10 Paramita system, the perfection is that of Skillful Means needed to overcome Mara who provides opportunities for others to act in opposition.
It is said that once the 7th Bhumi is attained, the Buddhas prophesy concerning your achieving Buddhahood, and will indicate your Buddha-Name and circumstances.
In a former life, Lord Shakyamuni received this prophecy after having presented 4 golden flowers to the Buddha of that aeon .
8. "The Immovable": At the Eighth Bhumi, you can enter Nirvana at the snap of a finger; so Tathagatas come and click you out of it, reminding you of your aspiration and the work still ahead. But they cannot force you to remain, therefore the virtue is that of firmness of Aspiration.
You might be reborn as Brahma, Lord of the Universe.
9. "The Good-Wisdom": Almost ready for Buddhabood, you practice the acquisition of the Ten Powers and Six Supernatural Powers. You might also be reborn as Brahma.
10. "The Dharma-Cloud": All the Buddhas and Bodhisattvas rejoice in your elation at having attained Buddhahood completely. Primordial awareness [dhyani/jnana] clears away whatever subtle defilements and tendencies might still be retained. You, like Lord Maitreya in the Tushita Heavens, await your turn. This is also the beginning of the Path of Non-Meditation.
I don't know if there is one particular place on this path in which all tulkus could be placed. But certainly to have gained the merit and wisdom to deliberately navigate the bardo in order to fullfill the bodhisattva vows, someone is certainly on the path.
Some tulkus, such as His Holiness the Dalai Lama is believed to be an emanation of a bodhisattva called Chenrezig. He is the embodiment of compassion. A bodhisattva such as Chenrezig forgoes nirvana until all beings have been liberated.
There are practitioners within Vajrayana who don't necessarily believe that all tulkus have realizations. Some people feel this is open to opinion. So I'm sorry, I can't give an entirely cut and dry answer. But I hope this helped.