Don't bother with the hub motor. Seriously... DON"T use a hub motor. A hub is lots of unsprung weight in the back wheel and your scooter has suspension, so use it and you have a nice place to mount a motor in the frame. A far better option is getting an outrunner such as the C80100 which is rated for 6kw. I know what motor you have already and the C80100 is about 60% the size of that BOMA inrunner and good for 2-3X the wattage. It will easily fit in the same space as your factory motor. You wil lalso need to upgrade to 219 sprockets and chain.
You have a giant battery bay. You should easily get 30-40 miles range and top out at around 50mph with the right set up.
This is a Chinese scooter similar to yours that I upgraded. It runs at 82 volts and I've speed tested it at 60mph! On level ground it tops out at 50mph and out accelerates most cars.
https://endless-sphere.com/forums/viewt ... er+project
Since your deck isn't flat, this will be more of a pain to do, but you will want to seal up your deck to the battery bay to keep dirt and water out. Also, that will give you an extra inch or so of space for more batteries or whatever inside the battery bay. I'd probably make triangle pieces to fill in or level out those low spots and make a new deck that was flat.