I aplogize for my lack of info ,i just switched from pc to apple and have yet to recover alot of stuff.
The last trike i made for a guy in madison we found 26 inch wheels from a garden cart supplyer in vermont . The wheel is hollow core with 3/4 inch roller berrings. So thats the main diff 3/4 vs 5/8 inch axle . Now we did it to save cash ,if your in a better cash brackett you can check out used wheel chair wheels from a medical supply place.
They generaly have 5/8 berrings,and some have great cap nuts and roller washers, yep you read that right roller washers. And some other cool parts like the parking brake .
I have a tendency to make as much of the gear as i can myself , so the bikes end up as one offs ,that can be a real bother if you plan to sell the bike when your done with it but will deff save you some serious cash in production.
I like to use a combo of cantalever and bolt on tech for rear triangle and generaly make the drive sprocketts out of old coaster brake parts .
For the most part the 44 tooth sprocket from kit fits cheap hubs then you just need to grind the locator ears off a rear coaster brake sprocket and then weld the two new sprockets to hub , but use a dial ind. Or you'll never get them straight.
I set up the lathe with two live centers and lett the hub self center on the berrings, then run ind. On spoke flange to figure out if it's true.
This step is prob the hardest part of the whole project , and I'll be glad to help you make up the parts if you pay for shipping ( I almost never charge guys from the forum for labor) sorry for the long winded answer ,hope it was some help.