As things stand right now, I don't foresee any reality where Rondo & Bradley aren't the starters, barring trade or injury. They have history that shows them to be a very effective back-court duo that has proven to be successful in the NBA. They are also very complementary skill-wise on both ends of the court.
I'd expect them to each play on the order of 30-36 minutes (again, barring injury).
That will leave 24-36 minutes at the PG & SG spots for Smart/Thornton/Turner/Pressey/Young/Johnson/Babb/Bogans to all fight over.
Obviously more than likely the last three names won't really be in the picture. So the fight is really more likely with just Smart, Thornton, Turner, Pressey and maybe Young.
Unless he has a strong training camp and pre-season, I expect Young will likely get at least some time in Maine, which helps alleviate a bit of the crunch. Plus, if he grows a little, he projects long term at SF. For now, let's leave him out of the picture (even though he's likely to get SOME big club time at some point).
Smart and Pressey are the only true 'PG' options among those guys while all the others are much better options at SG than Pressey, so by position, you are looking at the following for bench depth:
PG: Smart, Pressey
SG: Smart, Thornton, Turner
It should be possible for Smart to end up with the lion's share of those bench minutes, probably about 15 mpg. That would put him on line for about 1100-1200 minutes, which is very good for a non-starting rookie. Probably too few to get him ROY consideration though.
Obviously, any injuries or trades could shake things up.