As far as the resort being self-contained, I guess it depends on how well prepared you are when you check into the resort. If you do your grocery shopping on the way in (there is a Publix, Sam's Club, Piggly Wiggly and Harris Tetter all on 278 before you turn off into Shelter Cove where the resort is located) plus there are several restaurants within walking distance (like Scott's Fish Market where we had a great seafood meal). I noticed a lot of people riding their bikes around the island, including to Disney's beach house located at Palmetto Dunes across 278 and to several area restaurants.
There were so many activiites at the resort (swimming, ping pong, dolphin discovery tours, storytelling, campfires, etc.) that we rarely left the property except to go to the Hilton Head Diner and some outlet shopping. As far as the resort having "Disney" touches, they are there but more subtle than you would find "on property" which suited my DH perfectly. When you first arrive and get beyond the gates, there are a Pooh and Tigger topiary and I think they have a list of hidden Mickey's throughout the resort but there are no characters (at least not the Mickey and Minnie variety).
The two bedroom units are laid out wonderfully and your friends will enjoy having their own "studio" type accommodations. I spent a bit of time in the "studio" portion of our two bedroom to get a feel for it and I think DH and I could be comfortable staying in one in the future, but of course, I would prefer at least a one bedroom for the space and that fabulous jacuzzi tub.
We spent 6 days there this trip and it was definitely NOT long enough. We are planning a trip for next December and plan on spending 10 days starting December 26th. Anymore questions, just ask away!
Lisa