The best (in a performance sense of the word) way to limit the roll is with spring rates, but if you're running KW V3 I would definitely get a rear bar in. When stock, our cars heavily understeer (like pretty much every other stock car), but they can be made to have pretty good handling with some money and effort. Since you're doing all those kick-ass parts, I strongly recommend that you get some Defcons (preferably the Ultimate kit), and go with the MadMax control arms. The Defcons make a significant difference in handling - especially for the minimal cost!
Top all of that off with awesome tires and good, performance-oriented alignment, and you will be amazed at how your car handles