Hubs
The QS3000 motor at 13,800 watts overpowers some aspect(s) of most standard bike hubs. With Shimano rear hubs the free hub fails first.. After you weld it the engaging spur twists off the hub and you need a wheel rebuild, but with what hub? Likely with this motor you will make a one-speed.
Earlier Grantmac recommmends OSET hubs
https://shop.osetbikes.com/hubs/
As for the 6 bolt mount the OSET hub has for a drive sprocket, the pattern seems a little insufficient as I have sheared this same 6 bolt pattern running my Cyclone 4K at about 7Kw.
I am currently working with this steel hub as a spare wheel in case my DT Swiss 350 hub fails.
A variant kit of this HD hub from gas engine suppliers:
https://www.bicycle-engines.com/solid-sprocket-hd-axle-kit-w-brake
https://www.grubee.net/collections/traps-bullet-and-box-1/products/hd-axle-model-1-with-freewheel-hub
But there are other folks working on building stronger hubs. Gemini Bicycle Products may soon have an aluminum heavy duty hub
See: https://m.youtube.com/watch?v=X-DCXN-aYEg
Another heavy duty looking hub is the Jitsie which is made of T7075 alum (shear strength 48,000 psi))which is somewhat stronger than generic T6061(shear strength 24,000 psi).
https://trialssuperstore.com/products/jitsie-rear-wheel-race-hub-135mm
An real heavy duty rear hub from Jitsie is in the Moto category. It may need some shaft/dropout additions to fit a normal 135mm dropout.
https://www.jitsie.com/en/wheel-hubs/47956-hub-rear-wheel-race.html
White Industries makes a similar hub to the Jitsie Race Hub but out of T6061-T6 (shear strength 38,000psi)
If you build a HD hub that has 1 3/8" x 24 RHT there APPEARS to be a useable HD Steel adapter from Grubee with the 6 hole disc brake pattern but it will not fully thread onto the English thread. The reason it does thread for some distance is that a metric thread pitch of 1.0 mm is 25.4 threads per inch which is close to 24TPI. Plus a diameter of 1.375" = 34.9256 mm which is also quite close to the 35mm diameter.
https://www.grubee.net/collections/skyhawk-2-cycle-all/products/hd-axle-hub-for-disc-brake-attachment
Gearing Ratio Changed
I got a chance to try a lower gear ratio for hill climbing with the QS3000.
Ratio is 42/14 x 48/19 = 7.58. This makes for less front wheel air time. The bike and me at 155lb cannot quite do a standing dead stop burnout(front wheel against a wall) but with the slightest unweighting the rear wheel gets loose and spins. The ratio seems like about the right choice for hill climbing and my weight.