Are angels separate beings entirely from human, such that angels don’t become human, and humans don’t become angels?

This is entirely true. They are a separate cohort. They have differing soul makeup and they have different paths and purposes. The angelics were created to serve human and other life forms, so they are divine assistants and essentially will work strictly in close interaction with Creator to instruct them and direct them, and so have little independence, except within a small area of influence or responsibility that is a direction from Creator, to be their duty for a time. They are not a creative force on their own to create new paradigms. In that regard, they are inferior to the divine human, who are specifically intended to expand the possibilities of the universe with new creations, new paradigms. They will continue receiving angelic support for this undertaking, but it will always be led by the humans and not the angelics. In that respect, the angelics are the faithful servants of divine human. This is not meant for them to be seen as lower in status, but only different in purpose and in makeup. Such rankings have no value because one is always dealing with apples and oranges. One is not superior to the other. Whether one is desirable is subjective and whether one may have a superior role in a particular circumstance, does not mean the other is of lesser value in another setting. It is like with people, not everyone shines in the same environment. Not all are equal in their skills, and knowledge and talents, but each has a role to play, each has strengths as well as weaknesses. All are different in some respects and will have a unique makeup and signature in what they do. Angels have variations and differences as well and this is why there is a hierarchy that serves to keep an efficient organization of duties where those with greater reach have more of a supervisory function and those of lesser reach may have smaller areas of responsibility in keeping with their range of potential influence. It is no different than humans who will self-segregate according to their attributes where those with leadership potential will step forward and create a following. And others may simply join in and tag along quite happily to add their strength to the cause through their presence and participation, but not as being in charge of the undertaking with the latitude to make key decisions that could influence the outcome in a dramatic fashion.