I am working on a hub motor for picoFarrhad. I have purchased a stator off ebay (search for “atv stator” or “quad stator” to find something a little larger than what is usually found in old printer motors) and am now in the process of deciding things like number of windings and magnet sizes.
Since I am a n00b at this, I relied heavily on this instructable written by Charles. In Step 6 of this instructable, Charles gives an example of how to determine the desired motor performance, and then how to build your motor to fit those specs. I then made a spreadsheet that helps you do this: Hub Motor Calc. Feel free to use it, let me know what you think. It should allow you to play around with different parameters and quickly see how that will impact your build.
Next I will be ordering magnets. The sites I am looking at are: