don't do this out of HS. You'll miss out on more than you know just to save a couple years. Undergrad is designed to widen your gaze academically as well as socially. Also, you must remember that if you do well in collage, you can apply to better schools- don't sell yourself short NOW just to get to work longer. Giving it a shot will cost you two years. NOT giving it a shot might cost you the residency (and thus specialty) you desire... because lets face it, you have a far better chance getting your choice residency after a US school than after this one.
84% is still a B average, which while not stellar, isn't bad. You can get into a descent school with it, and try improving there.
As for size... it varies by year. ~30 is the size they gave you for the 6yr program, but you also have the 4yr (40 my yr) the BIS, and that's only for american. You then have the asian programs, a european one and of course, a sizable contingent of Polish students ^_~ If I remember right, one of my profs said she had 180 groups (~10 students, though i think the polish groups are closer to 30), and she might have been talking only of foreign students.
As far as med schools go, this place isn't small at all... which translates to schedules some of us would rather avoid.
If you apply, you'll almost certainly get in; HMI wants your $.
There's no entrance exam per say, but you do have an interview (although i'm speaking from the 4yr perspective... you might), and as for fees, look through my old posts and you'll find a couple where I copied my financial shcmatic for this year.