If you are renting an ECV, you will want to check out post 2 of the disABILITIES FAQs thread, which is about renting wheelchairs and
ECVs (link to that thread in my signature).
There was a change as of November 1, 2012, which involved WDW designating some ECV/wheelchair rental companies as "Preferred Companies".
Only these companies are allowed to drop off and pick up ECVs and wheelchairs from Bell Services. Other companies will need to arrange directly with the renter for delivery and pick up.
Bell Services will also store ECVs for guests renting from the preferred companies.
Asking for 1st floor for Medical Reasons usually works fine. When making requests, whatever is listed first by the guest is what the room assigner will think is the most important. THe more requests, the less likely it is that all the requests will be filled. So, list the most important first and limit the number of requests.
The only way they will guarantee a room is for the accessible rooms (that is required by the ADA because there are a limited number of accessible rooms and people who need one need to know ahead of time that they will have one).
Since OKW is only 2 floors for the most part, there is a good chance of getting first floor even without requesting it.
If you want to be totally sure, the only ways are either with an accessible room or going to a resort that does have elevators. Keep in mind that OKW is much roomier than the other
DVC resorts. We always have to move furniture at SSR to get DD's narrow adult wheelchair from the entry area into the dining area/living room. There is a lot more room to get an ECV into the room and some place where it can be charged at OKW.