The rattles from the trunk are corrected enough with Dynamat and make sure your license plate frame has something behind it to keep it from shaking too much. Honestly my friends who have got their 2012 hardly even notice.
I miss my 07 that I sold but I liked my old legacy and chose to keep it instead of the newer WRX ... so I sold the WRX and got the lady an outback with the spare change which she loves... I miss the WRX for the the HP boost it had but that is about it, my legacy is way more my style these days.... don't let the 1st and second gear bother you but learn to rev match on the down shift. Also suggest you avoid jackrabbit starts / launching I never had trans gear problems when i drove mine for the 38k I had it for but missing a shift was a PITA.... take it easy and you will be fine...enjoy your wrx and make it yours