you'll have a blast.
make sure you walk the course as many times as you can (5 times wouldnt be too many). maybe follow a experienced driver to see where he walks, ask questions. if you club allows it, get ride alongs with other drivers. so you can have a "high speed course walk".
Autox is a very novice friendly course, even if you did make a fool of yourself, nobody would say it, because we ALL were that fool once in our race careers.
as for power, i would estimate 140whp or below. stock these thing have ~110whp. and i just cant see those mods giving a 30% bump in power.
for auto-x: '04 Liquid Grey ZX3
for street: '02 Infrared SVT