Yes, those were my thought's entirely - looks like my first error (I'm more electronics/mechanics rather than software!) is with the arduino library, which was not set to port 50000 and TCP/IP (now fixed), but still no luck so far. I rather suspect it's how I send the data to the server from the serial that's the issue here: as INDI seems to 'connect' but cannot parse the data, I get the ekos error "[ERROR] Error getting device readings: Connection refused".

Tinkering continues ... at least for today!