Have a look at these articles on turbophile:
CA18 Street TunerProven recipes to get your CA-powered S13 cooking CA18 shakedownits also been my general understanding that to run a reasonable amount of horsepower (200rwkw) the most you are going to need is forged pistons(posibly not even these), upgraded turbo/injectors, front mount intercooler and a tune.
Check out this website for turbo's as well. I think their prices are better than average:
horsepowerinabox.com