I absolutely love this stuff. Just to add on here.

I highly recommend checking out the RC2014 project and it's various derivatives. Mr red fedora himself, Alan Cox very active on the mailing list: https://rc2014.co.uk/

Also check out the gigatron: https://gigatron.io/

I don't see this one mentioned much, but I had a lot of fun with this relay computer kit: https://www.tindie.com/products/jhallen/single-board-relay-c...

Someone else already mentioned Ben Eater's youtube channel, but it's worth noting he has two kits. One is a built out of logic gates, the other is 6502 based. https://eater.net/

Moving up the stack a fair bit, the commander X16 has a lot of people patiently awaiting it's arrival: www.commanderx16.com

Finally, there's plenty of stuff on Tindie. Here's one I've come across not too long ago. Note I have no experience with it and this is not an endorsement: https://www.tindie.com/products/glitchwrks/glitch-works-8085...