1) These stars are made by the folks who write for the recruiting site and publications. We appreciate they service of information they provide, but most of them are just huge fans like us that do this part-time or some full-time. They are not football experts, and neither am I, unlike an ESPN NFL panel or something.
2) History proves they tend to adjust stars up or down depending on who offers them. Hence, my argument of which comes first...the chicken or the egg? For your top players (5 star types) there is little argument because they are considered can't miss by all and cannot hide. However, the 2-4 range can be interchangeable and are best left to the paid coaches to determine their future performance. It seems players in this group are given a higher star count if a major school like UGA wants them compared to a staff like GT who wants them and could be better at evaluating talent.
3) Best thing to do...there is so much film out there...take a look yourself and see how good you feel.
Again, the 5-stars are probably just that. That is why you see the FSU's, Miamis, SoCals, UGA's, etc. put so many in the NFL draft in higher rounds. Some of these kids may not have even performed up to their ability in college but just continue high "recruitment" because of measurables. After them, you have to trust the coaches.
