Hi, Keri!
I think you will find that Walt Disney World is very mobility-friendly wherever you choose to stay. When booking your resort room, make sure to indicate your needs so you can be accommodated with a first floor room and a
room with ample accessibility.
Do not just do this at check-in, as those rooms may already be occupied. By booking your room with your special needs noted, you will be assured of proper accommodations.
You might want to choose a resort that is on the smaller side for the least amount of walking to the bus stops and food court. I suggest you look into
Port Orleans French Quarter. It is a Moderate Resort, so the pricing is reasonable and regardless of your room location, you will be close to everything.
If your dad will need a
wheelchair or ECV, they are available for daily rentals in the parks. If he needs one for the length of stay, you may want to look into an outside rental company that will deliver one right to your resort.
It sounds like you are thinking ahead about this so I am sure with proper planning your dad will be able to get around property just fine to enjoy all the magic of Walt Disney World!