Re: 1st build
Welcome to the forum, Marcelao. If this is your first motorbike build, I would get a kit motor and mount it on a steel mountain bike or beach cruiser. Mounting the hot KTM mill will require welding and the fat motorcycle tire will likely require that the engine be mounted offset to the motor chain side (not centered in the bike frame). You will also have to cut and weld the exhaust pipe.
If you have the welding and fab skills, or a friend of yours does, build the hot KTM. Otherwise, I think you will be on the road much sooner with a kit motor on a bicycle.
“You're only young once, but you can be immature as long as you like" -Unknown