Good for you! Have a great time! The only thing that's a "must see" is the Hall at Patriots Place (and the Pro Shop if you want to get some Pats' stuff - the end of the tour of the Hall "conveniently" ends in the Pro Shop). Everything else is just run-of-the-mill stores & restaurants. If you want to eat at a restaurant instead of tailgating, try Tavolino (Italian, not too pricey) or Skipjacks (seafood, pricey). Enjoy!
PS - My seats are in the 200 level and I've sat in other seats around the stadium. The views in the 200's are the best, IMO because you are high enough that no one in front of you blocks your view, but not so high that the players look like ants. I don't drink beer, so don't know the price, but everything in the stadium & Patriots Place is expensive, so bring a 6 pack to drink in the parking lot with everyone else!