Yeah I think you don't need to do this to an expensive bike. Mechanical disc brakes and just a front shock are probably fine if you want to go 50km/hr. A heavier sturdier frame and burlier tires are ok because it is powered.
I wouldn't recommend converting a road bike as they are more fragile.
Mechanical grip is entirely a function of tire compounds. In fact, ebikes can have even more tractive grip because you can make them AWD! This makes them much safer in snow and ice compared to other two wheeled vehicles.
They are fine at 45-50 km/hr. That keeps pace with car speed on residential roads fairly well. Any faster and I agree you could look at scooter or moped.
I wouldn't recommend converting a road bike as they are more fragile.