My DD uses a wheelchair, and we have stayed various places (none on the monorail, though, due to budgetary constraints). One thing that came to mind as I was reading your post was that your family sounds like they are still adjusting to your husband's needs. And if you are going to be on vacation, you want to do everything you can to be sure things are fun and go smoothly. So, some things to think about:
*It sounds like transportation is a big concern for you. Is there any chance you would be renting a car? Or will you only be relying on WDW transportation?
*The monorail is very easy to use in a w/c. However, there are ramps to get up to the monorail to board it. How does your husband do going up and down long ramps? My DD once wiped out going down a long ramp. It wasn't that steep, but she picked up too much speed too quickly.
*The buses are a little trickier to use, but not too difficult. The biggest problem with the buses may be the wait. Depending on how busy it is, you can wait for quite awhile.
*It might be worth seeing where the accessible rooms at Poly/Contemporary are located. If they are far from the monorail, that may not be very helpful. However, if you can get a room very close to the monorail, I would think that might be worth the extra money, at least for this trip.
Hope some of these ideas are helpful to you!
Mary