OK, thanks for the explanations. No, not hundreds of pieces of equipment in the plant, but eventually 15 to 20, and each with 5 to 15 sensors monitoring various parameters. The data is coming from 4 sources: Modbus 485 devices, Modbus RTU devices, Opto22 devices, and Raspberry Pi's.
I plan to organize my Modbus data using the buffer-parser (that you outlined here) and assign tags before sending to Influx, and for the Opto22 and RPi's, send it to Influx using tags. So on the same piece of equipment that has both Modbus and non-Modbus data, I will send separate measurements with meaningful tags, and few (if any) null values. I will use the Join/Trigger nodes only in those instances where it absolutely makes sense.
There are many posts on MQTT & Influx here on the forum that I should be able to get the data organized, but am I correct to assume that MQTT payload & topic would correspond to the Influx field & tag, respectively?