I feel that I should say that while in some MK attractions you go in th exit (such as IASW), you do not usually have any shorter a wait... most CMs make you wait there the alloted amount of time, or you may wait that long because there is someone with a disability ahead of you. they can only allow so many people with disabilities on at a time for safety reasons, and so you may be waiting longer than the posted times.
In many MK rides, almost all EPCOT rides (only one that comes to mind is SE), all DHS and all AK, you will wait in the regular line.
if your husband is in a park rental, you will have to push him the whole time. it will be too heavy for him to push, and they are heavy and old (50-60lbs). there will be no cushion on the seats, and the footrests will not be adjustable. if he needs his foot elevated, you will not be able to do that in a rental chair.
my suggestion is to talk to his dr at home about renting a chair there. trust me, you never guess how much walking there is in airports til you are on crutches... if you rent from offsite in orlando, you will have the chair the whole time (it is sometimes up to a mile of walking from your car to the tram, up the monorail ramp, down the monorail ramp and to wheelchair rental at the park - it is on the other side of the entrance from the monorail/boat... i dont think Daddy Tigger wants to hop that far)
also, if you talk to your doctor, your insurance may cover the cost of the rental. this may also make using an ECV more manageable. i think your husband will become very sick of being pushed all day long. also, if you are pushing him, you cannot hold your daughter's hand or push her in a stroller. this may be a problem for you, so i would definitely look into a scooter for your husband.
if he is going to be injured for as long as you said, you may be able to purchase your own scooter and have insurance cover it, cause he may need it at more than disney
PM me if you want more details of life in a wheelchair at disney - i have done it before!