a)
Using /follow (/script FollowUnit("party1") is the bes idea) is the best way to move, with WASD or other keys your movement will be directed to wherever your characters nose is pointing, which even on two identical computers will be near impossible to handle perfectly. It's bugged right now and disconnecting followers, some people are not affected by it, so pray that you are one of the few lucky ones.

b)
You should be able to use mice just fine, via software or hardware. I haven't bothered to config multibox/synergy to that degree, as I have the second computers mouse easily accessible for quick acts like looting, quest turnins.

c)
Feels like they are too far apart. How much is your paladin going to gain from the enemies the warlock can kill?