Newton is so close to Boston that, in reality, it often feels like a part of the city. You're tied in by the green line on the T, so that helps. But with that said, it would likely be easier for you to find more art-related activities in Boston than you will in Newton. However, that doesn't mean you have to live in Boston. It does, however, mean that you'll probably be spending a lot of time in there. It probably would be easier for you to live and go to school in Boston than in Newton, if this is a concern. But again, Newton isn't exactly far from the city. And there's no guarantee that, even if you go to school in Boston, you won't end up living in an apartment in Newton (or a town like it.) :LOL:
Some of the art schools in Boston have ties to the MFA, the ICA, and other art institutions. Thus you'd be able to get into those for free. Also, many, if not most, of the events on campus will be free to you, or of very low cost.
For access to the MFA and ICA, I prefer Mass Art and the School of the Museum of Fine Arts. They're right next door to the MFA, and a short T trip away from the ICA and the gallaries of Newbury Street. The MFA runs some fabulous programs, and I haven't been back to see the new ICA yet, but I've heard raves.
The better art stores are in Boston. Pearl, which I think is in Cambridge, is one of the best. You'll probably get a discount at at least one of the art stores with your student ID. They'll tell you about this when you start class.
As for social life, a lot of that depends on which school you'll be attending, rather than its location in Boston v. Newton.
I don't know which schools you are considering, so I can't talk about them. If you can tell me which ones, I can probably be quite specific.