Glad you found him/her! I agree with Steve, keep until spring. It's already cold enough I probably wouldn't release one where I live and I'm way further south than you.

Hm... I wouldn't brumate. It shouldn't affect the snake's ability to brumate in the wild if you release it, and being active/eating all winter will give it a better chance to grow and be larger and healthier for the release (or if you're keeping it as a pet, there's no reason to brumate unless you just feel like it). Plus, with wild ones you never know if they've got some sort of parasite or health problem that might make brumation more dangerous.

As far as feeding, you can probably wait till it's up to correct temperature for a few days to a week before offering. I mean, I see no harm in offering food now if you want to, but between getting too cold and being in a new place I doubt it'd take the food right away. Just try everything to see what it'll take. They can be picky.