So I got the keyboard, I got an Arduino Pro Micro clone and I even found a module which should be able to do C16, C64 to USB. Didn't worked on the first try.
But then... By reading into the whole HID thing I stumbled over HID as an attack vector, and then over the whole USB attack topic. Yes I have a Hak5 Bash Bunny now, as well as a RasPi Zero W running the latest P4wnP1. And found a frigging hilarious USB hub, with two device ports, to weaponize.