We've been there many times, and you MUST stay onsite. You not only get FREE Express Pass, but also Early Park Admission to IOA, and free transportation via nice water taxis. Universal offers a lot to do. They have two theme parks (IOA and US), but also have their equivalent of DTD, Universal CityWalk. Personally, I like CityWalk better than DTD, and you are sure to have a great time. If your son likes thrills, than you can't be at Wet n' Wild. This water park (a free bus ride away from the onsite hotels) is Universal-owned but not on property. They have a beach area for the adults, and amazing slides for the kids. If you stay onsite you also get access to the Golf Universal Orlando program, which gives you complimentary transportation, and discounted golf at some local courses. Best of all you get to wake up when you want, have an enjoyable breakfast, and head to the parks. Universal also offers a great character breakfast (ask your teen, he may like it) and they have a seasonal firework show, Universal 360.
I would spend three days and three nights with two day tickets. You could go to US on day one, spend day two golfing, relaxing at your resort, and a Wet n' Wild, and day three at IOA. Unviersal has three hotels: Royal Pacific, Portofino, and Hard Rock. Your teen may like Hard Rock, but I like Portofino (I love Italy and it is a luxury resort).
As for dining, I find Universal meals tend to be better than Disney. If you plan on eating primarily in the parks than you will benefit from the Universal Meal Deal (Universal's dining plan). I recommend making advanced dining reservations on opentable.com for all table service restaurants. Just select Florida>Central Florida Area>Type in Universal. Here are my picks for best restaurants:
Islands of Adventure
Quick-Serivce
-The Burger Digs
Table-Service
-Mythos
Universal Studios
Quick-Serivce
-Universal Monster Cafe
Table-Service
-Lombard's SeaFood Grille (on select nights you can watch Universal 360 here)
CityWalk and Hotels (only have table service)
CityWalk
-Emeril's
-Hard Rock Cafe
Portofino
-Mama Della's
Hard Rock
-The Kitchen
Royal Pacific
-Islands Dining Room
Have a great trip! Any additional questions, just ask!