If weight and comfort ain't priority, I would think about motorcycle wheels.
Most modern motorscooters have small diameter wheels with BIG diskbrakes. My scooter has a 12" front wheel and a 14" back wheel. But the big tires make them as large (or lager) as a 20" bike wheel.
I use the way the Bafang is set up to let the electronics dictate how much power I put in myself and how much the motor will add. In each setting the motor will assist up to an certain rpm. It's unfortunatly a tad higher than I like to pedal for longer distances, but it's a worthy goal to achive.
Hello there. Welcome back to the pack.
There is a reason why aluminium framed upwrongs use oversized tubing. Rule of tumb, , for the same wall thickness, increase the diameter (or square) with 50%. So a steel 1.5" box section will need a 2" or even a 2" 1/8 box section replacement. Thicker...
I would use a combination of Closed cell foam as bottom layer (think black industrial insulation foam) with a second layer with ventilation channels cut out.
On the other hand, I do like my mesh recliner.