ESP32 based webserver on separate WiFi network

Likely I will use an ESP32 board with the PSRAM once those are supported for JSVars in order to have more memory to store historical data

The esp32 build has 1mb devoted to a flash file system. That should be plenty of space to log to, with no extra hardware. The normal fs module and file objects work as if it is an sd card. If you buffer to ram, and then write 4096k chunks, it should be pretty easy on the flash.