@SpaceCowboy, the more “non-original” mods you make to your printer, the more comfortable you will need to be with the process of building and installing firmware.
The best way I found to get comfortable with the process was not change the printer at all and go through the steps of building the firmware that is currently loaded. This allowed me to make sure I had the software installed and configured properly and once I loaded “my” version of the firmware, if it didn’t work correctly (i.e. exactly like the original firmware) then I knew exactly where the problem must be. I didn’t get the build right.
In your case where the printer isn’t completely functional, you may have to improvise a little, but don’t change everything at once and then try to make it all work together (hardware and firmware).