Short throw shifters are nice, but if you like the stocker I would hold off on an aftermarket shifter for now. If you dont like the stocker, try and find a Mustang with a short throw and see if you like the short throw. MGW is the best there is, but they are expensive for just decreasing shifter travel and automatically finding 3rd gear.
Id get a midpipe first, then a catback so you can get the sound department taken care of.