Not sure on your experience level with the GM 3800, but did you assemble the shortblock yourself or have a machine shop do it? If you didn't have it align bored and whatnot then you may end up with the "200-mile motor". Meaning it will grenade itself in under 200 miles. The bottom ends on these motors are tough/expensive to get rebuilt properly, which is why most just get a used one and go from there. Rebuilding one of these properly isn't like a Chevy 350.
You could run an intercooler. You want the hottest spark you can get w/o seeing KR (knock). I would stick with the 3.8 pulley until you have the ECM tuned for the top swap. Even stock the S/C cars have knock. With a top swap you raise the compression which makes it that much more prone to knock. You need an Aeroforce or another way to scan the motor to see what the knock is, among other things. Once you have it tuned good, then consider dropping pulleys. If not then you could end up just chipping pistons and trashing the motor all over again.
If you haven't read the "Safely modding your 3800" thread on here, that would be an excellent place to start to answer your questions.
