Alright. Had a long day at work and couldn’t respond sooner.
As I have stated before to get started you need a RPi3, and RS485 to TCP converter as the hardware list, assuming you have the easygen 2500 panel then installing the emonCMS image onto the sdcard to establish modbus communication with node-red application the use JSON to publish to emonCMS.
Now to answer your second post, yes you can have arduino and modbus under each RPi3 your choice but the simplest way is interfacing instead of splicing into analog signals. Issue I potentially see with tapping into analog signals from the panel is the voltage drop you will encounter when connecting to a analog signal. Say your RPM gauge says 1500 RPM and you tap into that signal, you will read 1400 RPM give or take because of voltage drop, and the genset panel will read 1400rpm and will mess the signals going to the panel controller. Just giving you a heads up.
Like I stated earlier all commercial gensets have modbus available, it’s a matter of figuring out how to communicate to it. Some are easier to interface than others but it’s the correct way of doing things. I have never seen tapping into analog signals of me integrating genset systems for 6 years.
Yes the TCP converter is a cat5e you can connect to a switch, both the TCP converter and the RPI to communicate via TCP.
Your choice at this point but I highly recommend modbus, once it is setup, you will love it.