If I have the stage 1 star kit, how much better would it be if I put a stock gs-t intercooler or gsx intercooler on it? Or would it be better to buy a new intercooler, and what kind of extra piping would I need? And could I get it from the car I'm getting the intercooler from, or do i need to buy some?

They are good intercoolers. But if you have the money go with the starr intercooler kit or perhaps a starion or spearco..either way it is some work.

If you're going with the stock GS-T\X sidemount IC, you'de be much better off using the ones from a 1G instead of the 2G. The 1G cores is much thicker than the 2G's, more cooling capacity. I've heard that the 1G sidemounts are one of the more efficient IC's, except for front mounts, of course!!!!