I have been to Universal many times and we always stay at one of the 3 onsite hotels because of the Universal Express. You show your room card at just about every attraction, and you get into the express line. With Harry Potter opening, you may want to price out the hotels for the heck of it. September tends to be a little less expensive and the Royal Pacific Hotel is their least expensive of the 3.
As far as a shuttle, I don't believe they have one other than maybe recommending you to Mears. When we go, there are usually 4 of us and we use "Orlando Transportation Services". They are a privately owned taxi service, and the owner, Marty is one of the nicest people around. He is very accomodating, and always there when he is supposed to be. We don't rely on hoping a cab is somewhere we will be when we need it. It is nice to have a reservation for a pick-up or drop-off ahead of time. One time we were staying in Universal and took a day to go to Disney. He picked us up by 7am for us to make our breakfast res at Contemporary then at around 12am picked us up from magic kingdom after the Christmas party. Didn't have to worry about getting back. His website is orlandotaxiservice.com. For a trip from MCO to Universal, it's about $49.
Hope this helps. Have a blast!