Very little, The bicep mainly acts as a stabilizer during the movement. The Delts and Tris I believe are more "active" in the bench compared to the biceps. Of course the pecs are doing most of the work which I'm sure you knew.
yeah, your biceps are really just acting as stabilizers, so the triceps can function normally.
bench press is a pushing exercise, so triceps shoulders and pecs are the movers...biceps and the lats in the back are stabilizers.
no, but having warmed up biceps and lats will help you stabilize better, avoid injury, etc.
thus in my routine, bench comes after pull-ups. that's how i like it.