I have (for the most part) finished the project. The web site and node code are fairly complete, as well as having done some more experiments. It turns out that the D8 pin on the NodeMCU ESP8266 is the problem, not the 3v3 pin as I first thought. That means I can salvage my current PCB's and make some new ones without the need for a SPDT slider switch.

There is some more code for just testing a node. I am having problems with some of the boards that I ordered from eBay and Amazon, where they throw this error:

warning: espcomm_sync failed
error: espcomm_open failed
error: espcomm_upload_mem failed
error: espcomm_upload_mem failed

I have found a diagnostic web site and a blog that have proven useful in some cases. I'll try to find a consistent solution.