I printed everything with PLA on a Prusa MK3S.
Most of these parts have a lot of overhangs, and require supports. I printed breakaway supports, and was actually pleasantly surprised at how well this worked, and that it was relatively straightforward to remove the supports afterwards.
I sliced most of the models using Prusaslicer. To make the supports easier to remove, I printed with a 0.2mm Z contact distance for the supports, and a 100% XY contact distance (as a function of the external perimeter width). I used 2 top support interface layers, and 0 bottom interface layers. I also expanded the support pattern spacing to 3mm, just to reduce the amount of support material printed.
I wasn't able to get Prusaslicer to avoid printing supports inside the screw standoffs--even with support blockers, it still ends up generating supports inside the screw hole if it needs to support something else above the screw standoff. In practice, this wasn't a big deal; the support material inside the screw holes is not very much, and could be removed carefully with a drill bit.
Prusaslicer did not do a great job generating supports for the main underlays that hold the switch sockets, so I sliced these using the Cura slicer. It's tree support functionality does a good job adding supports for this part, and they broke away fairly easily, despite the fact that this part is somewhat thin and fragile.
For wiring the keyboard, I used 28 gauge Soderon 155 from TEMCo. This wire does not need to be stripped prior to soldering, which saves time since there are a lot of keys to solder. It has a nylon insulation that will melt and act as flux when soldering. Note that it requires a minimum temperature of 390 C.
The diodes can be installed in either direction, as long as you are consistent throughout.
For my boards, I assembled the diodes with the anode connected to the switch, and the cathode connected to the row wire. I connected the rows to bank A of the SX1509 (pins 0-7) and the columns to Bank B (pins 8-15). Bank A therefore needs to be configured as open drain, and bank B as pull-up.
See wiring.md for more notes on the connections to be made.