How to setup a local multiplayer game?

I'm trying to make a local multiplayer 2D brawler. Although I'm new to this type of genre, I have a few questions...

1. How should I setup a controller script assigned to each player? If possible is there a controller assign script?

2. Should I have separate tags for each playable character?

3. If every character is set to the same collision-layer (instead of a unique layer for every character), how could I prevent their own hitboxes from hitting themselves?

4. With Unity's One-way colliders, is there a way to drop through the one-way collider and have the character's floor collider not snap back on top of the platform?