Help with Fighting Game

Help with Fighting Game?
Hello, me and a team of developers are using UE4 to make an upcoming fighting game. We have most things on lock, but of course, in any game you develop there will be hiccups. So I wanted to list a few things we needed to solve

-Paper2D, Side Scroller Template or neither? This game will have 3D characters on a 2D plane, can we do that with paper 2D.
-Collision Checks and HitBoxes, how can we setup hitboxes or collision. When we are motion capturing should we just record the damage and the motion at the same time, or record them seperatley, or just a physics system
-Player Input, how can we have say for instance: X (PS Controller) is punch when the opponent is standing, but when the opp. is grounded play a different attack since the person is on ground.
-2 Player, how can we make a local co-op system so that 2 people can play on ONE screen, not split screen, but one screen.
-Multiplayer (online) How can we set that up?

It may just be 5 bulletpoints, but very important for this game to be a success.