1. Search. This has all been answered over 9000 times before.
That said, do not get a piggy back
ECU. A Link G3 is a full replacement
ECU which is good. Other options are Autronics and Motec as aftermarket replacement
ECU's. The best bang for buck option is a Verso re-tune of the stock
ECU (other option is ECUTek).
Also, you play - you pay. Don't expect much warranty work when you have exhaust, aftermarket
ECU and a boost controller. Subaru will only cover warranty on those parts not effected by modifications.