I only spent a year in Oxford for grad school and then transfered out. So, take this for whatever it's worth.
1. Oxford is a very small college town. Essentially for groceries you have Kroger (which is on the Miami bus line), and Walmart (which is not on the bus line). Your primary source of entertainment will be the bars in Uptown. For other forms of entertainment/shopping, you'll need to leave Oxford. Hamilton is about a 15 minute drive away that will have some better shopping/entertainment selections, but not much.
2. You can get decent apartments for relatively cheap. You really need to actually visit Oxford to find the deals though. Many apartments don't actually advertise their complexes online, so a visit there will be useful. And you'll want to visit the apartment to see how close/far it is from the Miami bus line. For pretty much all the apartments you would only have a 15-20 min walk to campus, but in the winter you might want to be able to take the bus. Also, I found that most of the loud undergrads lived right by the University in the residential areas where there are numerous houses for rent.
3. Can you survive in Oxford without a car? Absolutely - but realize you'll be limited to what Oxford has to offer, and you'll need to find a ride if you want to go to Walmart. If you need to get a transportation hub, such as the airport in Cincinnati, you'll also need to find a ride. FWI - the airport is about a 45 minute drive away and is quite nice. Don't hold me to this, but I think the University might run a shuttle back and forth to the airport - I can't quite remember.
I actually enjoyed my year in Oxford. It's a decent little town that can allow you to do work in relative peace and quiet - not to mention the campus is absolutely gorgeous. But, if you need something besides peace and quiet, Oxford won't be the place for you.
Hope that helps