Really it depends completely on the position. But will try and answer.
1. Really depends how good the pieces are and how many targets/open lines the queen has.
2. Would take the 2 pieces in the opening/middlegame, less likely to in an endgame.
3. If there's an extra attack, the pawns are passed, or it creates some sort of weakness. Otherwise no. I think people are too quick to do this in general.
5. 2 rooks are probably better if they both have open lines and the queen doesn't have targets.
6. I would trade 2 knights for 2 bishops, not vice versa in most positions.
Very simple here...assuming all things are equal in position and material...
1) 3 minors for Queen
2) 2 minors for Rook(assume not but situationally? ie active rook for
Bad bishop and knight, etc)
3) break a staunch pawn chain w knight or bad bishop for a pawn or 2
4) 3 minors for a queen
5) 2 rooks for queen
6) 2 bishops for 2 knights or vise versa