Nice questions from you Leo. I have been doing this in my spare time only, I have some answers to your questions ready. But I was considering making the twists per inch (tpi) totally user controlled / adjustable using a dial. So, this approach allows the end user total control while maintaining simplicity of use by the turn of a dial. The idea would allow you to spin off a short length onto a target or test bobbin and measure the tpi on the length between spinner assembly and the target or test bobbin using a caliper. Dialed in and loaded for production run are we? I think this is the way to make sure everyone will be happiest although it requires a little extra step its very worth it.
Yes. Although I've not tried it yet, multiple diameter wire should work. So far I have tested it with 36AWG film coated and was able to guide the twisted pair through a wire guide down range and onto a bobbin without breaking the wire. So, any length we are able to fit onto the two spools shown in the photos will work. Its definitely intended for other than fence wire though. This is a tool being calibrated for use to the electronics trade.
I hope that helps. I am on a limited budget also but I will continue to develop the project in spare time until its complete or until a development budget is made possible and then I could really pull it together.