The first part has been addressed a lot before in the thread, but I'll recap. Honestly, I've had no problems with security. Really, if you stay out of sketchy areas (read: north Saint Louis or in East Saint Louis that is technically in Illinois across the river) and don't walk down the street alone at 3 AM, it's not much of a problem. The only thing that may be a problem is cars getting broken into if you don't park in secured parking (at the school or at apartments in certain areas... that said though, my roommate has a nice car and never uses the school parking garage and hasn't had a problem with break-ins).
I'm a second year at SLU, and I would say our class is definitely close. For a class of ~175, I know nearly every body's name (other than the few people who make it a point not to come to class or hang out with med students) and feel comfortable hanging out with most everyone. I think it says a lot that there are very few people I don't genuinely enjoy being around. Everyone helps one another out. People will stay after anatomy dissections first year to teach others the material, they'll send out their charts/mnemonics/etc. the week before a test, etc. There's always class social events (med school prom, laser tag, sky zone, bar nights, karaoke, sporting events, etc), and a good portion of the class ends up going out together post-test. I have more of a social life now than I did in high school or undergrad and have made some of the best friends of my life.