I think one approach would be to assume it's a machine for beginners and therefore cannot require access to a mill or lathe to make.

If machined parts are required, there should be a source for ready made parts, ideally as I mentioned above, parts that can be made on the same machine.

Maybe another approach is to start with a Chinese ebay machine and provide a step by step guide to upgrading and retro fitting it... Maybe that create a narrower scope and prevent the impossible search for a 'prefect' machine that suits everyone.