UG, I am so sorry about your health issues. I think you should still be able to enjoy your trip. I am not anything close to a marathon runner, but I am fit and active, and work out 2-3 hours per day. 2 1/2 years ago, I injured my knee several months before a big Disney trip. Despite physical therapy and a knee brace, it became evident that my knee was not going to take all the walking in a Disney trip. Reluctantly, for the first time in my life, I used an ECV. We rented from an outside agency, they deliver to the hotel and pick it up. There are several companies, including Deckert's. We have used 2-3 different companies and never had a single problem. It took me just a few minutes to learn how to drive the scooter, and probably an hour to feel like I mastered it. If you can drive a car, you can easily drive a scooter. If you want, try one out at a grocery store to get the hang of it. But seriously--don't worry about the learning to drive it part. Easy cheesy. The only hard part is dealing with people who come to a screeching halt in the middle of the flow of traffic. Always be ready to stop suddenly. There are tons of people using ECV's in the parks, so you won't feel strange at all.
Last DL trip, I was sure my knee was better enough to handle the walking. Several hours into it, it was obvious that it wasn't. I was glad that I had rented a scooter just in case because I would have been miserable.
We have done lots of the different packages on 3 trips now with an ECV. We haven't been since the new 60th shows started, but every show and package we have been to has a way to accommodate the ECV's. WOC has sections for wheelchair/ECV users and their families.
For the rides, you take the ECV with you. Some of the rides in DL you have to go up the exit. But you don't have to get out of the ECV until the last minute generally. If you can walk enough to transfer, it is easier, but they will accommodate you accordingly. Like at Peter Pan, you go to the exit. I leave my ECV at the end of the exit because I can walk that far. Some people take their scooter or wheelchair up right to the point of getting on the ride if they can't walk that short distance. The CM's are always very accommodating.
You will love VGC! We love the Grand and are new owners at VGC, so excited!
Please let me know if you have any other questions. I would recommend calling now to book a scooter. It will save you so much pain and exhaustion on your trip, I promise! Have a wonderful time!