I think posing questions and answers anyywhere, and commenting in one's own discussions should require no reputation threshold, and be allowed anonymously.
Commenting elsewhere should require a reputation of +0 in the main section, and a reputation of +1 on meta, and should not be possible anonymously. Otherwise the discussion is open (in principle) to people that only do politics and no physics.
Up- or downvoting should require everywhere a reputation of +1, since it requires a minimum of good judgment.