I'd be even more worried about the ability of the stock suspension to handle the power, that is, keeping it down on the road during spirited driving.
The mod chain, in order:
You can make a WRX almost as fast as you want. All it takes is money. Vendors mentioned by others are a great place to start, but do yourself a favor, and drive a properly broken-in WRX first. It is only then that you'll know how the car is, and what it might need.