To be honest there is not much to it, you buy the movement, put it in a case, and put the hands on it. you can get everything from aliexpress. it's easier and often cheaper to just buy a normal watch if you need one.

I thought so too, but after quick research apparently there are kits. For various values of "DIY", I guess...

I had one, broke 2 screens before I gave up wearing it... It's really not meant to be work in daily life, which is sad because an e-paper screen makes a lot of sense on a watch.