My wife loves her 7.2 and has been commuting 7 miles daily for the last 9 months and just had her first flat last week. The 7.2 has worked flawlessly. You do not need disc brakes, but if you do get disc at least get hydraulic disc over cable disc due to hydraulic require no adjustments. The higher up you go in the FX line the lighter the bicycles get. Not sure if you are going to an actual Trek owned store or a privately owned Trek dealer, but when I bought my 7.5 I was given a little discount off the MSRP. You might want to check other dealers in your area. Plus you can also look for last years, 2012, models left over.
We have Magic Shine headlights on our bikes and really like them, I have actually had cars flash there high beams at me when I have had my light adjusted to high(pointing to high), puts out a lot of light!
Have fun looking at and test riding all those bikes!