I'm not sure what exactly you're looking for but ai03 has a PCB design guide which you can follow. For physical design of the case, I like to start at Keyboard Layout Editor, since that gives me a visualization of the layout, plus I can use it to help with firmware stuff and case/plate design, with the help of ai03's plate generator. The ras pi interfacing stuff I don't have anything to help with off the top of my head. But reading your other comment, that can already be done in QMK, just make sure the keyboard layout on host side are all consistent and voila. For instance, my Reviung39 runs a custom workman layout that's tailored to me and as long as host side all use standard US intl layout, it works all the same regardless.