Wheels...
Buy the round plastic tubes from evergreen. Largest size is .5 inches diameter. Use that as your outer hub. The spokes can then be made with flat, hex or round plastic strip.
Build up the tire with very thin plastic strip of .015 thickness. Takes a bit of time, but within the hour you have a sandable plastic tire that can fit your hub.. you can also criss cross or lay down stripes of plastic on your last tire layer before you wrap it around, and you have your tread pattern.
For more precise spokes, you can drill small holes in the tube rim, and then thread through plastic round strip or wire, using putty to lock them in a central hub.