Update: My #24 checked out fine with the voltmeter, installed all ICs and tested via the USB serial interface (as I don't have the RCA video connector as mentioned above). I use Minicom on Linux, everything works. Krusader, monitor, Integer Basic and Applesoft Basic. Been a long time since I last saw that ] prompt..

It took a few extra days before I could test it, my old laptop computer only has USB 1/1 and 100mA so I figured that would be insufficient - didn't take any chances. But yesterday I got a powered USB hub from a nearby shop, it can provide 1A per USB socket. Working fine!
-Tor