ok allot of questions there. I'll answer as best as I can, look at this site. It's a real technical site with lots of good information. It's not just a set-up for one RC car but basicly a good guild line to go by for all.
A stiffer sway bar will generally give you less traction because what it is doing is not allowing the suspension to roll. By not allowing it to roll it's not allowing it to put weight on the outside tires while cornering. Your car is constantly balancing whether braking, cornering or accelerating.
Roll center does change with Camber link location. Check that site for Chapter 2, it has an awesome explaination. Also Roll Center changes by placing shims underneath the ball studs. Your Roll Center ( Camber Link locations ) will effect the amount of Camber change during your suspension travel. ( up and down )
Rear Toe end will settle your back end, give you some more traction. I wouldnt go over 2 degrees.
The important thing to remember is this. Your car is under constant balance, your front end and the back end. What ever you do to one end will have an effect on the other. As they preach do one change at a time and test it.
Check out that site, its very helpfull!