I didn't know any of the other med students when I was accepted last year (and went to college out of state), and now one of the people who I hang out with the most was literally the first person I met on the first day of the optional enrichment program last summer. It is true that the class size is large in the Twin Cities where I am, but I would not worry at all about making friends (even if you are the shy, study-all-day type). Everyone is super friendly, even if they happen to be someone who you don't talk to very often. Plus, even though many of the lectures are optional, there are also weekly mandatory sessions (including small group ECM sessions and occasional FCT sessions) which have ~10 people sitting at one table with a professor/preceptor. These small group sessions are a great way to get to know people in class early in first semester.
Starting second semester you are also learning more in-depth clinical skills for a few hours every week in groups of three, so you get to know them really well too.
TL;DR version: The class size is large, and I don't know everyone super well, but I don't think it limits class cohesion and I wouldn't worry at all about making friends
Since we have a no pass/pass/honors grading system, and "honors" is only determined by earning a certain percentage of the class points (no class curve, class rank, etc.) it is a super friendly, cooperative environment.