First off--deep breath and welcome to the DIS. Everything will be fine, you're going to Disney.
The fact that you are staying at the Grand Floridian is a big help, because you can get to two parks (Magic Kingdom and Epcot) very easily. For MK, just board the monorail at the Grand Floridian station--you will be there in a minute. To get to Epcot, continue on the monorail through the Contemporary to the Transportation and Ticketing Center. From there, take the monoraail to Epcot, or catch a bus to Studios, Animal Kingdom or a water park.
My advice: when you check in, get a brochure for each park--they will also give you a brochure with park hours, parade times, etc. Since you don't have a plan, why not do one day each for Epcot, MK, and Studios, then split a day between Animal Kingdom (morning when it is cooler) and Blizzard Beach in the afternoon. Then use your remaining time for Universal or repeats of WDW parks.
Just remember, you cannot possibly do it all in one trip. Pace yourself and enjoy what you can. While it might be impossible to get priority seating for character meals this late, guest services at the Grand Floridian can help you make dining arrangements. Also, they should be able to help you with a shuttle to Universal.
Have a great time (I hope your hip feels better) and let us know how it goes. By your next trip you will be a pro if you use these boards.