Thanks! The main difficulty & goal with this one was reducing the power consumption to the absolute minimum, which meant putting some effort into component choices and I also ended up writing the display controller driver myself.
But if you just want to get going, you don't really need to go through that sort of trouble. You can just buy a panel + controller board via a retailer like e.g. Waveshare, and hook them up to a computer. Quite a few of these controller boards even have HDMI input, or come with SDK code for e.g. Raspberry Pi if they use SPI over GPIO. You can tinker quite a bit without things getting more challenging, and if you can arrange for wired power you may not really need to optimize anything.
But if you just want to get going, you don't really need to go through that sort of trouble. You can just buy a panel + controller board via a retailer like e.g. Waveshare, and hook them up to a computer. Quite a few of these controller boards even have HDMI input, or come with SDK code for e.g. Raspberry Pi if they use SPI over GPIO. You can tinker quite a bit without things getting more challenging, and if you can arrange for wired power you may not really need to optimize anything.