Hi Christine,
I'm so sorry to hear about your feet - hopefully you are on the road to mending 100%. The parks are pretty flat - there are a few slight slopes here and there but for the most part they are flat. I think that the biggest slope that comes to mind is at the monorail stations. That being said, the parks are really big, especially Animal Kingdom and Epcot and there is a lot of walking involved.
If your husband is in pretty good shape, I'd try going with a wheelchair instead of an ECV. I think that it is easier to maneuver in the crowds with someone pushing a wheelchair that in an ECV - especially if you are not used to using an ECV. It is also cheaper to rent a wheelchair which are $15 per day ($13 per day if you purchase a Length of Stay ticket) vs. $45 per day for an ECV which also requires a $20 refundable deposit. If you start with a wheelchair and decide an ECV is the way to go, you can always try an ECV later on.
Wheelchairs and ECVs are available for rent at all 4 of the theme parks and DTD (rental for an ECV at DTD is $45 per day and the deposit is $100). There are also a limited number of wheelchairs for rent at the water parks.
Wheelchairs and ECVs are available on a first serve basis and are limited to you'll need to get to the parks early in order to secure one. You are not allowed to take a rented wheelchair or ECV from park to park - they must remain in the park in which you rented them. If you park hop on a given day, you can take your receipt to the next park to get another wheelchair or ECV if there is one available.
You will be able to stay in your wheelchair for some attractions while others require guests to be mobile. For more details on mobility and attractions, click
here.
Wishing you magical memories :-)