Why exactly are you wanting to use DOS? Go with windows for sure.
As multiple controllers, you could do gamepad hacks for each controller. However, to simplify connections to the main box you could have one main control panel with an ipac 4 in it, and then have Parallel port breakout connections to plug the other 3 control panels into the 1p control panel. The controls would always be dedicated, and you could plug any panel into an open slot as you need to.