welcome fellow subaru owner
no need for the accessport if you are just doing a catback exhaust (no downpipe)
you will need a tune for an aftermarket downpipe.
the accessport isnt horrible, but it isnt the best. the maps that come with it are soooooo conservative that you will get bored with them after a while. if you want a really fun car, do upgraded suspension (sway bars, ed-links, bushings) and some good tires. also a good mod would be a short throw shifter with bushings, it will make a HUGE difference in the way the shifter feels (by far the best mod ive done for my car)
:thumbup