[Msquared]

For autocross competition the key to answering your question is what class you plan to run, and what mods they allow. If you're in SCCA classing, then stock your car goes to B Street. That allows you to change one sway bar, and most people swap for a stiffer and/or adjustable front bar to tame the slight power-on oversteer the car can have with full-bore alignment and all nannies off. I went with the BMR front adjustable bar because at its softest setting it's very close to stock, which seems like desirably option to have.

If you want to start modding for real, then consider CAM-C. I have a list of mods I'd do there (to remind myself why I don't want to go to that class!), and I'm happy to share if you want. My advice to someone just starting out is to compete for a season and use that time to gain skills and also to assess what class you really want to choose, and then plan your mods accordingly.