Okay, so - a few weird things with the serial ports. Win 10 doubled up on the same names (i.e. two COM 1 ports, two COM 2 ports) in Device Manager even though they all got different IRQs. So, I went in and renamed them COM 1 through COM 7 in order.
In the literature, 'COM A' is supposed to be the touchscreen serial data stream which is supposed to map internally to COM 1 by default. PuTTY would not let me open any serial port which meant a trip to the overly-intrusive settings in Windows Security to turn off a bunch of stuff likely interfering. When I came back to PuTTY I could open COM 1, and do indeed get a data stream when I touch the screen in different places. So all that works.
Device Manager is a bit of a train wreck. Win 10 did not find drivers for what it decided was 5 ethernet controllers and the Multimedia Audio Controller. Under Human Interface Devices it recognizes 3 USB Input Devices all with drivers loaded. I would have expected to see a Touchscreen listed there with a missing/ unloaded driver...so Windows either doesn't recognize there is one - or enumerated it as one of the USB Input Devices and loaded a generic USB driver by default.
I'll have a go at installing the drivers back down the thread a-ways and see what happens there.