Rofel:
Weekly Plainville events are as follows, with some very general estimates:
Monday: Magic Draft, between 8-20 players. Also, sizable LFR game.
Tuesday: Warhammer Fantasy is getting some steam, up to 8 players, and Magic Legacy, not sure how many people are actually playing, say another 8?
Wednesday: D&D Encounters, you will likely have little to no table space
Thursday: 40k. There would be enough room to paint, as the 40k people play. There is now starting Magic Commander league, but I don't know how big that'll get. But they'll take up some table space. I'd assume a dozen people to start.
Friday: Friday Night Magic. Yeah, no.
Weekends: Like Chase said, Saturdays tend have events, most of which occupy the greater part of the store. Sundays are generally quiet, if you don't mind the Pokemon crowd in the early afternoon.
Mondays and Tuesdays, there will be table space, maybe with some creative shuffling involved. Sundays would be free enough as well.
Wednesdays and Fridays are dominated.
Thursdays would be okay, depending on how big the Commander league gets.