as long as you have a new gasket, it doesn't matter what pattern you tighten them in, as far as i know. you can try starting from the outside, working your way in if you want to be safe, but i seriously doubt it will hurt anything if you don't.
You should definitely be able to reuse the stock gasket. I'm still on the stock one after 180kmiles and a turbo (back to NA now though). As far as tightening order, which ever way is easiest. The runners on some headers make getting to certain nuts more difficult if you tighten them last, so just keep that in mind.