Does anybody know for how much episodes for season six is Misha signed on - or in what episodes he should be?

I don't think they release that kind of stuff. I do know he is a series regular again this year. He was only in 4 episodes out of the first 11, but his wife and he just had a child and he was given time off. I heard him say in an interview that Castiel has a major role to play in the second half of S6 so there is reason to hope he will be a much bigger part of the last 11 episodes :)

Hope that helps, at least a little...I realize this is 2 months late.