While I do have spare Pi Zero expansion PCB’s for the emonTx4 and Im more than happy to send you one, there were a couple of issues with that design that might make it more trouble than it’s worth. The Pi Zero needing a separate USB micro power supply being the main one as I made the mistake of not routing 5V to the expansion header.
That’s much simpler, good idea! There are so many different ways to configure these things and sometimes a simpler solution like that is the best one. @borpin’s suggestion is also a good approach.
I agree on the ESP but I could not find my spare ESP boards and I did find spare Pi Zero WiFi - thanks for the pointer on EmonHub not EmonCMS I will try that.