Well, I can say two things about your questions. I was in the same boat, and had pretty much made up my mind that I would immediately put some mile axle backs on to get a throatier engine note. I also had long term plans to swap out the 3:31's for some 3:73's as the warranty was nearing expiration.
After having my car for this past weekend, and putting 190 miles on it....lol, I'm going to wait on the axle backs. Once you get around 3K rpm's, the engine sound really starts kicking in, and the car is plenty loud in the cockpit. I'm starting to think that for a daily driver like mine, louder exhaust may become annoying over time.
As for the gears, right now I'm happy enough with how the car handles and performs, that I'm second guessing the need for 3:73's.
Mustang base coupe, V6, manual transmission, Red Candy tint, performance package.
Upgrades: DSS aluminum driveshaft, BMR LCA's, Yukon 3.73 gears, MGW shifter.
Displaying 3.7 fender badges is like telling everyone your wife is "office hot."