Keeping your car in stock form and autox's will not be any fun. A car that handles like a dream is fun. The first and most important thing would be to go to coil-overs. and of course adjustable struts and shocks, lower chassis brace,strut tower brace, subframes, upper and lower control arms, some weight off the front end will help too, fiberglass hood, battery relocation. But coil-overs are the most important. Normal factory style crap doesn't do it good for autox or even drag racing. x2c coilovers can be had for something like $400 for all corners. But when you lower a car to much the a-arms become angled terrible and they'll need some help. Bumper steer kit, steeda x2 ball joints, offset a-arm bushings. And of course tires, not sure what to get on this though. But nitto makes a autocross tire thats the same compound of the dr's just with a stiff sidewall.
Josh