For safety reasons we recommend installing a fuse as not having one can be dangerous if there is a short circuit in the wiring. Using the fuse that is currently on the scooter would be much safer than not installing a fuse.
I just noticed the specifications that you posted. I would use a 50 Amp fuse, unless the scooter uses a fuse that is less than 50 Amps and then I would use that size of fuse.
I presumed that the scooter originally had a lead-acid battery pack with a wiring harness that has a fuse holder built into it. This presumption may have been incorrect though. Do you know if the scooter originally have a lead-acid battery pack or lithium battery pack?
I would install a 50 Amp fuse then since that is the maximum size fuse that should be used with the battery pack.
I do not think that the lithium battery pack has a fuse. A fuse holder and fuse would need to be installed between the battery pack and controller. the best place for it would be between the battery pack and its power output connector.
I was referring to a fuse that would be custom installed however if the scooter already has a fuse between the battery pack and controller then see if the fuse is 50 Amps or less and if it is then it would be okay to use.
Yes, that sounds like the safest way to do it. If the procedure is carried out properly then there is no danger at all. Just make sure that one of the polarities is fully insulated before working on the other polarity so this way if a wire is accidentally let go of then it has no chance of touching a live conductor from the opposite polarity.