No such thing as a stupid question (unless you have been told the answer before).
Did you use miniterm to set the serial to be on?
Did you set up an interfacer for the serial data? If not it is in the thread.
Are you going to use the emoncms on the PiZ at all? If not, in emonhub config, just point the MQTT interfacer to the main emoncms host IP.
Set the base topic to be emon/TX2/ or what ever so it loads the values into a node called TX2.
Just leave it as emon/.
I’m running a modified MQTT interfacer (PR submitted ages ago) so I cannot be absolutely certain the config parameters are correct. If not you will see errors in the logs.