Sonoff-Tasmota VS ElegantOTA

Also read https://github.com/arendst/Sonoff-Tasmota/wiki/Sensor-Configuration about support of sensors per group.

As u/__deeetz__ pointed out, the esp32 already had a good OTA mechanism, and there are some libraries that simplify the whole process - probably one of the more popular ones is ElegantOTA: https://github.com/ayushsharma82/ElegantOTA If I understand what you're doing correctly, you'll really have just 2 layers, not 3 - one being your application (which effectively has the Kernel/OS compiled in), and then your scripting/LUA component. Technically the ESP32 also has a bootloader portion, but it's pretty uncommon to need to modify that in any way, so I would highly recommend against doing that. As far as dealing with the LUA scripts - you can easily download and run those - you'll store them into NV ram, and I believe the current recommended format is LittleFS. Keep in mind that on a normal ESP32 configured to do OTA updates there's 4MB of storage, 2x 1.8MB for the two bootable images, and ~200k for the file system (in this case LittleFS). There are also other boards which come with more flash memory, like the new S3R8 has 16MB of flash, so your OTA partitions stay about the same in most cases, but you now have ~12MB of storage, which I suspect would be way beyond anything you'd need for storing LUA.

I'm looking for a small, thin example of the ESP32 hosting a webserver to accept firmware update files for OTA updates. There's a handful of Arduino libraries that do exactly this (e.g. https://github.com/ayushsharma82/ElegantOTA) but I haven't come across anything clean that's just built around IDF.