Until you can out drive the stock suspension Don't change it.
As for power leave it alone until you are used to it.
The only thing I would upgrade IF you have plans of doing HPDEs is brake fluid, Brake pads and maybe some tires.
then spend the rest on getting to HPDEs check out this site.. many people here use them : http://www.nasatx.com/main.asp or http://www.nasaproracing.com/