I have stayed with a friend in a wheel chair there are not elevators so you need to have a Handicap room. I think we were the first stop but not sure we never had a problem getting on a bus. The only time I have was with another friend in a ECV we were leaving the MK and there was two people already in line ( and no one else but there family) the CM at the stop called for another bus and about 5 minute latter the first buss came and 1 minute after this out bus came we were loaded and on our why before they loaded the second person in the ECV infant of us. I have heard that if you are waiting for a buss and can not get on because you are in a wheel chair ECV they will get another bus for you. This is the only time this has happened to us and we go a lot
Guests with wheelchairs or
ECVs don't need a handicapped room unless they actually need the features of the handicapped accessible rooms.
If you don't need the features like roll in shower, any first floor room will work. The doorways are no wider in the accessibile room than the regular rooms. The layout is the same except the arrangement of the bathroom in the villas with roll in showers.
OKW is the oldest Disney Vacation Club location. At the time it was built, there was an assumption that people staying at DVC resorts would spend more time in their rooms - so the rooms were made quite large and have plenty of room for an ECV.
Most of the buildings are only 2 stories, so even without making any requests at all, you have pretty much a 50:50 chance of getting a first (ground) floor room. Guests can request a ground (first) floor room for medical reasons if they want to be more sure. Many guests want to be on a higher floor for better views, so that figures in too.
There are no elevators. If you need a wheelchair accessible room, I believe those are on the first floor. There are varying types of accessible rooms and not all are first floor. So if you don't need a wheelchair room, I believe you will need to call and note your reservation as requiring first floor.
@SueM in MN has stayed at OKW with a wheelchair.
Enjoy your vacation!
My family has belonged to Disney Vacation Club since 1993 and our home resort is OKW. We've stayed in various locations at the resort with both ECVs and a guest (our youngest daughter) in a wheelchair. We go twice a year and our favorite area is Miller's Road area. There is a walking path to Hospitality House, which is about a 10 minute walk away from buildings 20 and 21.
Buildings 62, 63, and 64 have elevators. Near Hospitality House, but not HH area.
First stop for the park is Peninsular Road. Last stop before leaving the resort is Hospitality House, which is the first and last stops on the Disney Springs bus. It doubles as the internal bus.
eta: have stayed at OKW twice with an ECV. FIrst trip, I was assigned to a partly accessible room with a high bed I had to lie across and pull myself in. Moved next day to an accessible room with an accessible bed

at the far end of building 25 or 26.
The other trip, I was in building 13 - roll-in shower, typical height beds. Rather than try to move from such a great location, I called Maintenance. While I was out, someone came and took apart one of the beds.
Buildings 62,63 and 64 are kind of in a strange location - most of the building numbers are consecutive, but they are near the buildings in the teens instead of with the larger numbers.
That's because they were built after the rest of the resort after they tore down the original preview center and some other buildings that were in that location. Buildings with 2 floors are not required to have elevators, but those buildings have 3 floors and also being newer, required elevators.
Because of their location and having elevators, they are in high demand.
OKW does not share buses with any other resort. Even staying at Miller's Road, the next to last stop, we have seldom had wait for another bus because the wheelchair spots were all filled. There is a higher chance of a full bus if you are at the first bus stop (Peninsular) at a time when many guests are returning from a park (not enough may have gotten off yet). We've also found it full at times when we tried to get on at Hospitality House.
The bus driver will call another bus if they have to turn you away.