Thanks, Stephane, for your detailed consideration to my issues.
Sadly, though, I have given up on the Pi5 and ordered a Stellarmate Pro. The issues with their app don't concern me, I can use the device as I have been using the Pi, a NoVNC connection via Wifi, with a real WiFi antenna, better physical connection to my rig, offers me better hope of getting a working system going.
Two years ago, I was seduced by
this article
into thinking this would be easier than it has turned out to be. So many things could go wrong and so many did. We can rename Murphy's Law (if something can go wrong, it will) Cohen's law. Not just power issues in general, but so many of them! Every cable is a potential flaw. And no good way to measure it, though you provide some good clues here.
The other thing that got me thinking about Stellarmate was your mention that all you guys who are working on AstroArch are using an Ethernet, not a WiFi connnection. That is not an option for me, due to my location up the hill from a horse stable, which brings a lot of flies, so screens must be kept closed so ugly cables through the door are not a real possibility. Nor am I willing to rewire my house. So WiFi hasn't been tested as much as I would have hoped. I was the guinea pig. And the results were poor.
I like your suggestion of plugging the USB for the EAF into the camera. That never occurred to me. That I can try if the Stellarmate doesn't work out.