tl;dr the stock suspension is great as-is for track and autocross use, if it's your first time just go for it. In my opinion save the money on coilovers for getting brake pads for the track and better brake fluid as much as a $500 investment that is very much needed if you want to drive the car at >90% of it's capabilities.
The only thing you might want to do suspension wise before your first time to prepare for the track is a quality four wheel alignment, not a quicky place but a shop that actually specializes in fine tuning cars for the track/autocross.
From the factory the only thing that warrants improvement is front camber, typically it's less than -0.5 degrees, ideally for a true track car you want to be -2.0 degrees camber or more, this is not possible to do stock. The cheapest way to add camber is to get some "camber bolts" for the front end, this should get you to about -1.0 degree camber. This will help your front tires grip better and last longer on track for ~$20-40 for the bolts and $200-$300 for the alignment if I remember correctly. This should hold you over until you upgrade to whatever coilover system you decide with camber plates or some form of adjustability.
Save your money for brakes if you're serious about tracking.
At a minimum read everything given to you by the organization you will run with and read this:
http://www.ft86club.com/forums/showthread.php?t=25485