Disc Brake for Hub Motor (V3 QS)

Hi!

I recently bought an electric motor kit for a conversion im doing on an 1976 yamaha rs 125.This is the kit I bought.
https://www.aliexpress.com/item/Superpower-Ncyclebike-48v-72v-5000w-e-bike-conversion-kit/32725409177.html?spm=a2g0s.9042311.0.0.241e4c4dUaWmq9

My problem is that the kit doesnt come with a disc brake set and im not sure exactly what to order so it will fit.
Does anyone have any recommendations for this motor? Im slightly worried about the strength of it as I see most are advertised as "bicycle " disc brakes. Just to note I wouldnt want to be going very fast anyway, 100km/h maximum.

Any help would be greatly appreciated. Sorry if theres not enough information here to make recommendations, if theres any other information needed please let me know.

Thanks a million,

Cal

100km/h is very fast.
The kit you bought is for bicycle dropouts - ~145mm width, axle 16mm x 9mm.

Decide what brakes you will use. Heavy thick moped rotor disks or thin light bicycle brake rotors.

Moped rear forks usually have ~200m axles.
So few options:
-mill new 200mm axle for the hub
-ask qs to sell needed axle

If want to use current bicycle axle which is in the hub your bough:
-make custom rear fork for 145mm axle and use bicycle brake rotor

Regarding brakes. Hub cover is designed for bicycle brake rotor with 6 screws.
You can screw adapters and try to fit moped rotor but axle is short and not sure how it will work.
Bicycle quality brake braking power is too weak for 70km/h+. If you will have regenerative brake it might be as an compromise. Anyways you don't have much use from rear brake if it's not Harley style bike where your main brake is rear brake. Usually in regular asfalt bikes main brake is front and rear is less powerful because rear wheel has less traction during effective braking.