I use wooden stators, and wind the coils on wooden pegs, either round or square, depending on the magnets. I mortice or drill the stator for a good push-fit of the peg and adjust the coils for uniform height before glueing in. I use wooden cheek pieces on the pegs, of the exact size and shape of the finished coil diameter, pot the coils with waterproof glue, then cut off the cheek at the magnet end. A little extra protruding piece of peg is a coil-saver, because clashing magnets hit the wood first without damaging the coils.
I have used MDF, OSB, plywood and UPVC plastic for the rotors, and also for the stators, bolting on rings of iron behing the magnets.
So, it can be done (I am also, perversely using wooden bearings. but that is another story.)
How, or if, this approach would scale up into the 500watt class, I can't say (yet).
Still exploring and experimenting. Good luck.