-caster degrees ?
6-16. the more caster the more steering effort
-how much scrub radius ?
~ 25-40mm, none will give you no feel, too much will increase steering effort
-ideal king pin angle ?
more of a grey area. your limits are defined by scrub radius, the arms, the brakes etc. the more you have the (combined with caster) more your wheels will "flop" over when turning, which is a good thing. the longer you make the stub, to get more kpi, the weaker the upright is inherently.
-equal or unequal A-arm?
Unequal. gives you progressive camber change during compression. It's a very good thing, offroad.
-Any free software available to figure this out?
http://www.racingaspirations.com/?p=286