The heavy duty "rental" bike is called the
Atlas, available through the J&B catalog at your nearest bike shop. You could really beef up that bike, and still come out ahead versus the Worksman.
All the stress is on the back wheel and tire, no matter what you weigh, that's where you want to concentrate.
We had a forum member with similar concerns last year, (
? Big Roy ?) he (and
many others) contacted "
the wheelmaster", up in Washington State, to lace him a super-heavy duty rear wheel.
Here is his MB.link, and serious MB.ers will vouch for his work and the superior quality of his product :
@the wheelmaster
It is a great idea, on a single speed, to add front brakes before motorizing. This is YOUR vehicle, and coaster brakes by themselves just don't cut the mustard.
Purchasing that Atlas through a bike shop gives you access to add ons, like wide saddles, shock absorber seat posts, thornproof tubes, etc.