Ha! Another convert! Good choice, sir, and don't let the doomsayers on here tell you otherwise *lol* Hatches rule!
I assume it's all pretty standard at the mo? You can always go for a Prodrive Pack from subaru, but you'll be out of warranty anyways so this maybe isn't an issue for you.
Take a good look at Andy Forrest's site. Cat-back is OK and will give you a pretty good exhaust note over stock, but if you're shooting for those sort of numbers, you're as well to go for a sportcat or decat... you could always get one seperately!
I'd uprate your spark plugs and get a cold air intake - Litchfield or AEM are among the best - and I can strongly recommend Duncan Graham (raceDYNAMIX Time attack driver - Google it!) as an alternative mapper. He's mapped a lot of hatches (mine included) and has a lot of happy customers! He's based down south, but will travel all over... give him a shout.
Anything else you wanna know Hatch-wise, shoot me a PM.