im sure the fan will help, any airflow will help.
Id go for the 40mm stator magnets for sure if you can get that motor series ..
if you cant get that, there is always the magic pie, but cro motor would go nicely as well... but imho, id rather get a decent mars motor for that money
im pretty set on making one of these with a chain drive setup, would be super easy to mount a motor
20kw + there might be a chance of getting it to do dangerous power wheelies
Magic pie Dual Suspension
Peak 6kw Air cooled
Kelly controller (mini kbs series, smaller than a coke can, can do 80+ battery amps peak, Favorite small controller. Really punchy)
Safe, Beautiful handling.