1. what exactly can you do with a wrx limited before you have to start adding exspencive parts like trannys and injectors ect. keeping to fuel economy close to stock.
2. what kind of a job is it to change the cluster? might want to put an sti one in.
You should start by looking into some good engine management, I would suggest a Cobb Accessport...and then turbo back exhaust. 2, many have had swapped gauge clusters. Both of these topics have been discusses in depth on here and on nasioc, just gotta search for it.