On reflection I think there is a whole lot of re inventing the wheel, so to speak, that may not be needed
just looking on the web you can get wheel chair specific parts and chairs of various prices, qualties
your can get clearance wheel chairs pretty cheap
Manual Standard Wheelchairs - Standard Wheelchairs - Wheelchair Parts.Net
same place has bearings, wheels, axels etc.
Wheelchair Bearings at Wheelchairparts.net
Rear Wheel Axles for Manual Wheelchairs
Rear Wheelchair Wheels
sun rim wheels
Rear Wheels - Sun Spoke Rims - Wheelchair Parts.Net
easy to just replace a bearing
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Life is too short not to ride the best bike you have, as much as you can
(looking for Torpado Super light frame/fork or for Raleigh International frame fork 58cm)