If the empowerments reveals what is already present within us, why the need to get all these different empowerments?
To purify karma, purify the mindstream, to plant seeds, to bless beings, to introduce beings to the nature of their mind. These are the primary reasons (but I would like to see the list that Jamgon Kongtrul surely has in his Encyclopaedia but I cannot find).
And if the yidams themselves share the same nature why do we need to get seperate empowerments for different practices?
This is more on the method side of things - different deity practices have different results and have different power. WRT to compassion and the ultimate nature it's all the same (actually this is true from the side of the Buddhas and deities but not exactly true from the side of the being receiving the empowerment - different levels of tantra do reveal different views on the nature of mind for example which is why outer tantra takes 16-32 lifetimes).
It seems that any empowerment would allow us to practice a number of different sadhanas.
This *is* true for Highest Yoga Tantra but if you have some accomplishment. Most people don't have the confidence to pursue this and anyway it would be customary to receive the blessing of the specific practice (and would be a good thing).
Any why is it that certain sadhanas can be practiced by recieving only the lung, such as the way that ChNN gives transmissions.
I don't know how ChNN gives empowerments but some sadhanas do only require lung in specific traditions (even in Sakya where normally full (albeit brief) empowerments are given for just about anything).
I am not trying to imply that empowerments are not necessary, I truly want to understand the process more. I believe that they are more than just a ritual or a mere formallity.
Empowerments area a form of charismatic dependant arising. I would like to see the theory behind them presented from the Tibetan side (so this would be a mediaeval interpretation of this form of activity from the side of the written material but interpreted by living masters this becomes a real explanation). The primary thing is that they are a purification and an installation and that the master is enacting essentially a form from some sutras where they talk about all the Buddhas empowering a Buddha-to-be (so already a high Bodhisattva in this case).
And what if we happen to be sick or distracted during an empowerment? Or make an emergency trip to the bathroom? Can a sadhana actually be less effective or even useless if we somehow "messed up" or held the wrong view during the empowerment?
Wrong view is a problem but not the wrong view of the nature of mind (the minimal view is said to be the view of the Mind-Only school and the best view is one of the Madhyamika views). But the absolute minimal thing is compassion for all beings and better some dedication to a minimal Bodhicitta (so a minimal dedication to eventually liberating all beings at least in theory).
Distracted: this can be a problem but it just means that your personal experience during the empowerment was less than it could have been. Then again maybe not. You might have really gotten a glimmer of true compassion or another quality and this overwhelmed you. That's okay - take the empowerment again later (this is a Sakya view BTW - empowerments are themselves practice).
Sick: this is a purification during he empowerment. Usually this kind of thing happens *before* the empowerment.
Bathroom: some people would say that you missed some of the empowerment. I think it depends. Then again this is a form of purification and anyway you would get the main empowerment itself.
Engagement in the sadhana is self-correcting as long as you are sincere. Want to attain Buddhahood for all beings? Good to go. The sadhana will eventually open up to you.
And what if we got an empowerment, but didn't start doing the practice till years later?
Since you are not carrying the lineage of this practice then there is no problem. Afterall, the seeds are planted in the mindstream. Like a form of positive karma they remain forever (they might be overwhelmed by extreme negativity but will still bear fruit in future lives).
I think I am trying too hard to "figure it out." I have faith and devotion to my Gurus, but sometimes I second-guess myself after empowermets.
Faith and devotion is the key. Don't second guess yourself after the empowerment. If you meant to get it, you got it. Secondly you should start seeing positive changes in yourself over time.