MY DH has Crohn's, and one of the reasons we go back to WDW again and again is because he can spend the entire trip using a wheelchair without it seriously interfering with the vacation. He doesn't use a chair at home, but there's no way he could do WDW without it.
If his surgery was within the last six months, I'd strongly encourage intending to use the wheelchair for the entire trip - otherwise, by the time he "needs" the chair, he'll be too worn out to enjoy himself anyway. All the WDW resorts have chairs available for you to borrow for the entire length of your stay. (although avail. isn't guaranteed) You will have to put down a credit card or cash deposit of $200 (that's what it was in 2002) Call the hotel directly and arrange this, which is also when they'll tag you for a ground floor room if necessary. They'll put you as close as they can to everything, but with so many of the hotels, close to one thing is far from another thing, etc. so having the chair right there morning, noon and night is ideal. Disney trans. is also exceptionally easy for someone using a wheelchair.
There are also places in Orlando where you can arrange to rent a chair for a week, or you can borrow one at home and bring it with you. We've become quite accustomed to travelling with a chair, and have our own now. Except for Disney and major trips to Walmart, it sits in the garage most of the time, but we're glad to have it when we need it.