Given my tendency to start but not finish projects, I have made a good deal of progress on this project without making any updates. Now that the project is rolling and I think I'll actually finish, I'm going to start posting updates as if I had actually done them from the start.

This inspiration for this project is a pile of cool stuff (okay, mainly the printer) and a compulsion to finish something before buying any more cool stuff. I decided to purchase a 5" HDMI display because of difficulties I had in working with E-Ink displays in the past which are due in part to my incompetence but also the fundamental differences in their functionality and the needs of a computer display (static display with slow refresh vs. constantly updating). I haven't given up on E-Ink... just for this project it's nice to have a display done and working (albeit with a $60 price tag plus cable). The printer, display, a USB hub and a keyboard make the core of the system, pictured below (missing the Pi Zero):

The next big question is how to connect it all together. Data: HDMI to LCD, UART to printer, and USB for everything else. Power: while the display and Pi can both be run on 5V via USB, this adds a lot of cables. The printer also uses 5V, but at least 1.5A, so more than USB can provide normally. This led me to the conclusion that I need to make a "power distribution" module... which is an excellent place to put switches. Switches are necessary.

This sketch shows the relevant connections for each component. I also checked the pin outs / docs to make sure I could supply power over various pins and pads instead of USB cables. Oh, and I picked up a 5V 2A wall wart to provide power.

So, at this point I have a pile of parts and some idea of how they are going to go together. The next steps are going to be the physical layout / case, and the design of the power distribution box.