I had to position the models diagonally onto the build plate to make it fit. The print time for the case is around 16 hours. Support is needed under the slanted bottom of the case.

After the support is removed (by using a sharp knife for example), thoroughly sand the bottom using grids 120, 240 and finally 400.

Cut a piece of thin cardboard of the same size and shape as the plate. Push it into the case to avoid painting the inner parts, as this might impact the tolerances.

Apply a surface primer, then multiple coats of spray paint (I used Nippon Paint Pylox No. 65 Lily). To make it more durable, use a protective coating (e.g. Rust-Oleum Polyurethane).

Press all switches into the plate. Also assemble the stabilisers and push them through the plate from behind before snapping them in place.

Solder the diodes to one pin of the switches. Connect the switch rows and columns using the thicker 20 AWG solid core wire. Then connect the MCU with the flexible stranded 24 AWG wire.

To put the plate into the case, I use the following procedure:

1. Put the MCU board into the cut out. It should snap right in.
2. Insert the upper edge of the plate into the case.
3. With the bottom edge still lifted, use something like a popsicle stick to route the cables around the cylindrical sockets at the bottom of the case.
4. Lower the plate and snap in the bottom edge.
5. Press down all of the keys to make sure they are sitting snug in their sockets.

Then, secure the plate using self-tapping screws. Lastly, put the key caps onto the switches.

Install QMK and go through the initial setup process. To compile and flash the firmware cd <repo_root>/qmk_files from within the QMK terminal. Then

source compile.sh

That will copy the files to the right location within QMK and compile them. To flash it to the keyboard when asked, plug the keyboard in while holding ESC down. This will enter the bootloader mode.