Stay in ASP it won't be that bad
C Stock in Hawaii looks very competitive. I was running within .5 seconds of Tom Richards RX-8 with Hoosier A6 with my 370Z on stock tires. He's now running 3-4 in class against those BRZs.
If any mods I would go with a set of sways. Don't change too much at once. I also recommend sticking with street tires so you can develop good habits and a feel for what's going on (weight transition/power on off/when to brake/how much brake). Just have fun and get seat time in.
HOOAH!
**Oh yeah...if you get a chance to do fun runs look for Jon Matsushige in the black Camaro SS. Let him drive your Z. He will drive it like he stole it which will give you a new perspective of what the car is capable of. Just watch him and the course and take mental notes.