The next step was loading some code into the ESP-01. This module doesn't have a built-in USB-to-Serial adapter, so we needed to build or purchase an external adapter. Though we've built some in the past on a breadboard, we didn't want to deal with messy wiring, so we went for the latter of the two options and picked up a cheap ESP-01 programmer on eBay.
The thing is that we want to remove the header of the ESP-01 so that the LED board sits flush against its back side, so we needed to connect the programmer and ESP-01 module without using the pin socket. In such cases where we don't have a header to use, we turn to pogo pins for making temporary-but-robust electrical connections between PCBs.
Luckily we had some 2×4 pin-to-pin breakout boards for a different projects that came in very handy!
Our first attempt, without too much thinking was to create a 2x4-to-pogo pin sandwich board that we could simply plug into the header of the ESP-01:
Unfortunately this didn't work because we only have access to the top side of the ESP-01 as the pins on the back of the module are soldered to the LED board, which doesn't have pads/pins on its top site. As such, the connections are reversed by a mirror image.