Welcome...sounds like a great find! How many miles?
But first thing's first...if this is your first car then stick to it as stock for awhile. Chances are you don't have much cash, and you will be paying plenty for insurance. Learn to handle the car as is so you become a safe and experienced driver.
Once you have a year or so experience, then perhaps you can start modding. An automatic WRX will follow the same mod path as a manual for upping the power, so just search around. Stage 1 and Stage 2 will be your friends. Only things different...if you plan on doing a lot of dragging or so (legally!!!!) then transmission coolers are beneficial and performance torque converters. Happy searching!