You can have the schematics and my assembly code for version 0.1. You can easily replicate it on a breadboard and I can point you in the right directions to find useful tools like an assembler and an emulator. Zwölf 0.1 is very bare bones, so that the emulator can still be reconfigured to the few changes to the old Elf. That is really helpful to get you started. Unfortunately the emulator will become useless once I get more of the Zwölfy features working, but I'm already in contact with the author who wants to make the emulator more versatile anyway. Still, the processor is very different from the other 8 bit processors of the time and the emulator will probably be a great help to get you more familiar with it. Later, we will be on our own. Zwöf is a departure from the old Elf concept and therefore most old software and tools will not be very helpful anymore. We are mostly on our own, but that's part of the fun.
I have lived with several Zen masters - all of them were cats. His last invention was an evil Lasagna. It didn't kill anyone, and it actually tasted pretty good.