1)Everything bolts right up. No modification was necessary whatsoever. Use extended hangers but it will still touch the bumper. Right now it's cold so it's not melting but I intend to fabricate a bumper cut out from an 08/09 WRX Rear Diffuser...once I get my hands on one.
2) Yep. Just the catback. I have no engine mods as of yet. For the price that a WRX cat can be had for, it's well worth it for both the sound and appearance. I did not want anything loud or ricey, we're just 2.5s anyway. This is the perfect balance of a deep, yet subtle growl with a calm G35ish sound when accelerating. No drone either.
I may be mistaken but I could swear I hear a slight rumble when waiting at lights too.
Hope I helped.