Thoughts:
-I kind of don’t see the point of going to Michigan when you have been accepted to two excellent in-state public options. Indiana and Purdue are both great public universities at which you’ll pay resident rates, so unless you’ve been offered significant aid at Michigan (which it doesn’t sound like) honestly I wouldn’t consider it. It’s not really worth a comparative benefit, particularly if you actually do go to medical school.
-ALL of these schools have excellent research opportunities, and all of them will prepare you for medical school. You can’t really predict the probability of medical school acceptance from any of them - that really depends on your own performance more than anything else. Suffice it to say, though, that if you get the kind of record you need, getting into medical school won’t be a problem from any of these universities.
-If you are interested in the athletics scene, it seems to me that Purdue, Indiana, and Notre Dame are the best places to go for that (and Michigan, if we were considering it). Most large public universities have diversified social scenes that allow you to enjoy yourself outside of school and party; Notre Dame is also pretty noted for it’s fun social life. All of them are in small college towns so no real differences in atmosphere.
-Relatedly - not that UChicago and Northwestern students don’t have fun, because they do, but going to school (and partying) in a competitive environment with a bunch of uber-smart, elite students is a different environment than going to a public university with students of all stripes. Chicago and Northwestern (and Notre Dame, too, although perhaps to a lesser extent - because the atmosphere is different) are going to have that more academic, intellectual, fairly serious vibe most of the time. Chicago in particular is known for quirky, intellectual students. Indiana and Purdue will just have a different vibe - not that there aren’t quirky, intellectual, or even uber-smart students there, but there’s more of a range since they are large and public. Personally, I think there’s no shame in choosing the lower-stress, more socially-oriented environment if that’s what you want - I did, and if I were to go to college over again I’d emphasize those traits again. You can still get a really high-quality education. Some people also like being a big fish in a metaphorically smaller pond.
-Notre Dame is great but if it’s significantly more expensive than Indiana or Purdue, I’m not sure that the cost differential makes it worth it. It depends on the difference, though - how much would you have to pay at each? I’m 8 years out of college and I have a graduate degree, and as someone in that position I’ll say I’d rather have little debt from a less-prestigious undergrad than a lot of debt from a more-prestigious undergrad. If you do go to medical school, where you went to undergrad won’t matter so much.
-I think you need to wait for Northwestern and Chicago - they both have generous financial aid policies, so if you are admitted it’s quite possible for them to offer enough money to make them the same price, or cheaper, than Indiana or Purdue. Then you also have some geographic considerations, since Chicago is in Chicago and Northwestern is pretty close to it. Bloomington and West Lafayette are both only about an hour from Indianapolis, though. South Bend’s about an hour and a half from Chicago. None of that matters unless you have access to a car, though, whereas from UChicago and Northwestern you’re either in the city or likely have reliable public transit to it.