So I finally have the software sorted and I can "drive" the servos on the kitchen table by logging onto the Pi's network with my smartphone. A eureka moment of sorts!
I pause here to thank @Roger for responding with generosity and verbosity to my requests for help in the last few days. Thanks, dude. I dig your style.
Anyways, I did some dumb things on the way to this interim destination. I'll briefly lay out my errors below for the possible benefit of someone else having a crack at this project with the same limited exposure / ability as myself.
Misdeed #1: Save your edits. I evidently managed to skip this bit a couple of times even with the confirmation messages reminding me to do so.
Misdeed #2: If you are going to copy/paste rather than type text into files / command lines then make sure you select the whole text string / body - don't skip the last few characters.
Misdeed #3: When I edited the config_lewansoul.json file I got the format of the 4th line wrong - I missed the quotes on the path string. This is correct:
Misdeed #4: Well not so much a misdeed as a tip. If you run in test/develop mode on a laptop / PC then you may get an error message telling you that you do not have permission to access TTYUSB0. The answer is here if you run some variety of Linux: https://sudomod.com/forum/viewtopic.php?t=6075
Misdeed #5: if you don't have the Lewansoul Buslinker board powered up and plugged into the laptop / Pi when you point your browser at the appropriate address then you'll get Internal Server Error 500.
So, having achieved wireless control of benched servos, now I get to complete the mechanical build and get stuck into the electrical build. Noice!
Twenty eight days to Christmas...