Well ing my game each player could possibly control up to 5 mechs at once, with a max number of 4 players at once.
Making that 5x4x4000* = 80000 tris in a scene at one time. *approximately
That of course isn't taking into account weaponry and the battle area it self.
Since its my first 3d game, I don't want to overload my scene too much too be honest ^^. Always good to start low and then work up. Infact my vega model was only 2000 tris, so this is already an increase for me XD...