The Uchiha's are great even without the sharingan, the eyeball is only an addition to their terriably ninja-fitting bodies...
it was said quite early in the story that only a select few in the clan gain the sharingan (of course, it doesn't seem to make a diffrence since almost every uchiha in Sasuke's flashbacks has the damn thing)...

There's no indication on how many gates Gai can call open, it's probably above 2 (since he thought lee them), but other than that, your guess is as good as mine.
and if you're asking, I think that Gai can open less gates than Lee, and that's why Kakashi was so suprised when he heard Lee can open up to the 5th gate... well, that was what i thought 2 years ago, before the story turned crap... so gai can and will probably go 8th gate on someone's ass in order to save Lee from death.