A lot of people tend to want to cut corners but fail to realize what they are asking the engine to do.
You want street driven reliability, daily driven, and 500hp out of 2.5 liters.
This is going to cost you, and cost you dearly I am afraid. If you step back and look at what you are asking, it certainly won't be "easy" or CHEAP to do by any means.
If you take the price of a brand new STi + the price of the modifications necessary to obtain these power levels safely, you might as well have bought the Dodge Viper that you are building a Subaru to beat.
Just my 2 cents.