You aren't allowed to block a serve in volleyball.
No, a block is separate from the three allowed hits in volleyball. Also, someone who blocks is allowed to hit the ball again right after they block it.
No, you are not allowed to attack or block a serve in volleyball. If you did, you would give a point to the other team.
Yes, the libero can set. However the libero may not block, attempt to block, or serve.
Three, not including a touch at the block.
On the block, they are allowed to play it again if possible and they can double a ball on a hard driven ball if the motion is one fluent motion.
No, you are not allowed to serve with a fist in any level of volleyball.