DCS reads all input devices that Windows does. I imagine you will have a problem on a really old PC with an ancient windows version. I have 4 USB input devices apart from my wireless mouse/keyboard, TrackIR (and headset) I use Windows 10. Win7 will be fine as well. I dunno about earlier windows incarnations. But I don't think DCS will run on earlier windows at all.
Rewiring switches may not as easy as it sounds. I think it is too fiddly. But it is defenitly do-able. And HAT swtiches can be repurposed to 4 or 8 independant switches. I dunno what the Siatek software will do when it 'misses' switches.