Welcome to the boards! In regards to wanting to do AutoX, you will not just want to get lowering springs. I would recomend a decent set of full coilovers and various strut/roll bars to stiffen up the suspension. As for the wheels, it's really going to be a matter of preferrance. 16s aren't too bad as you can still get a decent sidewall w/ a good drop and not worry about rubbing. 17s would be a bit much, especially in the weight department but if autoX is going to be a hobby then just get some nice 16s and some good tires. As far as performance mods go, check out kfxperformance.com.