Learn on the E90. The first couple times out you will just be learning the line, flags, etiquite, etc. It will be sensory overload. You shouldn't be driving hard enough to shred your tires or breaks your first couple times out.
Not sure what you are looking into, but for the CCA events all you will need is a brake fluid flush, inspection and Snell rated helment to get out. Also look into track insurance as you may not be covered under your auto policy. Be careful though, this can get addicting, and if you become addicted, it gets expensive.