Indeed the Pi Zero is a v’good solution and I would always suggest the Pi ZeroW is used where someone is considering an emonESP, I posted on this wayback (4 CT emonBase using emonTx and Pi Zero W) and I know you are now a big fan too. But in this instance Julian has some old Pi’s kicking around, plus he has specified “wired”, although I doubt very much that the Pi’s would suffer any of the issues he’s experiencing with the emonESP’s.
@haffle, perhaps try one or more of the Pi’s you have spare, Ethernet first? Then Wifi perhaps and if the WiFi side is ok and you wish to streamline a little you could buy a couple of PiZeroW’s and swap over the SDcards, they are so cheap.