@sharpbeer, first off, those messages in the Arduino Serial Monitor look correct. Each message from the Arduino to the tablet (or Raspberry Pi if going that route) will have “KBSP v1:” and then some encoded string after that, so I’m not concerned there. The temperature messages and flow messages look slightly different and I think @mhmatttu has a good screenshot that illustrates that.
As far as the flow meters, the screw-terminal RJ45 adapter should work just fine, I was actually using one of those successfully as I was prototyping my build out. I would first connect your flow meters directly to the arduino to make sure they are working (maybe you’ve already done that) and then start testing with a cable in-between. I’m sure those screw-terminals are already connected to the pins on the RJ45 connector.