Howdy Vegas and welcome to the forums!

well... as you increase the number of class types, the complexity in controlling them effectively increases. it's not impossible, it's just tougher. (melee is possible, and helps you understand how to maneuver your characters better.. i rolled 5x warriors and 5x rogues.. its possible, but you can forget pvp)

as for why would anyone roll 5 of the same class... more power! (/tim taylor)

seriously, 5 mages casting 5 fireballs followed by a fireblast is pretty tough to endure...