So much pessimism. So little DIY adventure.
The local bike shop sold me a Schwinn in 87 that dumped me on the road due to a insufficiently torqued stem. They are good at tires, period. The bikes they have in stock are way to big for me except the single speed ones, useless on the 8% hill a half mile from my house. One bike shop over in Kentucky also has stock only for enormous leggy European/African people.
In e-bikes the heavier the frame, the better, within limits. So that junk steel the metal man is hauling off in his pickup truck, that is IMHO what you want. Caveat, the trash bikes are sized for kids, 18" stem to stem max, and adults need longer frames than you find used. I have native AM bones with short legs/long torso, and will be converting a nineties girls 10 speed soon to geared hub electric. Five gears (suntour) are too high for me, perfect for e-assist.
Internet bike parts suppliers, so far I've used niagaracycle.com. They are good at their big parts, but complete idiots at measuring small nuts to make them match up to the description. They can't read a machinist scale and can't even ship the same nut size twice on the same order description a month apart. They refund promptly for the trash nuts they send you. They shipped a shifter rod for a sixties Sturmey-Archer 3 spd hub right, so if the identification is unique they can do it. They are in NY for us east of the Mississippi that don't like UPS rates from Oregon/Calif.
Jepson seems expensive, competitivecyclist seems mostly tuned to light weight racing parts. Modernbike.com may get my next order. They are in Iowa.
I'm seeing a lot of facts on here about lunacycle.com kits, and their prices seem good. Descriptions are almost complete. They are in CAlif. ebikes.ca in canada has even better descriptions and support, but cross border shipping inhibits me from trying them. Plus they are in Vancouver, further even than oregon. UPS charges for milage.
Don't forget Amazon. They are not sophisticated and the descriptions are brief and maddening, but for generic things like spokes, brake pads, derailleur takeups, they are cheap and their warehouse is 6 miles from me in Kentuckiana. I've used them four times.