Hi Duncan and
to the forum.
You appear to have a pair of original Smart Pies, so you will need to use
the early type controller.
You will also need the controller housings and the rear fan/disc brake mount that are missing from your pictures.
According to GM China, the early Smart Pies are not compatible with the Vector controllers, so unfortunately the newer Bluetooth controller is not an option.
It should be possible to build the Smart Pie into 36 hole 20" rims, but the conventional crossed spoke pattern would result in excessive angles between the spokes and the rim:
To avoid excessive spoke angles at the rim, GM assemble their 20" wheels with all the leading spokes on one side and all the trailing spokes on the other:
A much better method of installing the Smart Pie into a 20" rim
(or smaller) could be achieved by drilling another 36 holes in the hub flanges as shown here:
This would allow a more conventional spoke angle with trailing and leading spokes distributed evenly on both sides of the wheel:
With a 72 hole hub, it would even be possible to fit the Smart Pie into a 16" rim if required:
The required spoke length will vary considerably according to the spoke pattern and actual rim being used.
You will also need the main wiring harness to match your controller connector along with a set of matching controls (Throttle, Brakes and Cruise button):
Hopefully I have covered most of the answers to your questions.
Alan