I think your better off w/ the offsite rental.
You are going to be able to move easier at the resort, move quicker to
get around the resort, get to the bus/monorail, boat (depending on where you are staying). Compared to walking w/ the boot on.
I would think that it would take more time if you were to try to walk that distance than use the offsite rental sccooter and then may or may not have an extra wait w/ the bus.
We've done scooter rental on several trips and most of the time 90% of the time we didn't have to wait for another bus because there were already 2
ecv's on the bus. Most of that was when we were at the boarkwalk area hotels, which share buses for AK and MK. But, never had a problem because it was a short walk/ecv ride to MGM and epcot.
Then when you get to the park, waiting in the line to get the parks ecv.
I guess I don't see the time saving by renting on site.
Plus, at the end of the day. YOur going to be happy that you have the offsite rental. I'm guessing the getting up and out of the scooter, maybe short walks, out of the scooter will probably have you tired, and maybe an achy ankle cause after all you have a broken ankle.
That walk to the buses, and from the buses to the resort room would not be good for a tired you and a tired ankle.
You will have a great time w/ your grand gathering.
Don't worry, having the scooter will be fun too. All the people in your group will be envious about half way thru the day when their feet and legs are getting tired.
OF course I'm sure you would prefer to be up and moving about on your own. Just take it easy while your injured, and you'll be feeling better after the injury heals. Just be patient w/ yourself.