How does it work for 4 players, are there any scenarios in base game for more then 2 players, or does it always work like splitting units between 2 players on one side.
The only 4 player specific scenarios so far are in Operation Cerberus. The current rules for 4 players are pretty basic - just split your units up but otherwise play it as a 2 player game.
The game works fine though with adding more players who all just play for themselves too. I've played multiple 3 player games where we just select units round-robin and then play the game, each of us playing for ourselves. It works quite well.