If you have a Zero, then you need to solder a header to it. If you un-sure about doing that then maybe you instead get a rpi3, in which case you may need a new case of it was for the Zero.
Did you buy this premade unit from someone via the forums? If so, then they should have already had it pre wired. I don't send any heatermeter to anybody without first knowing there ability or I make sure it's ready for them to use.
As for the cat5 cable, I'm currently at work and unable to give you the correct wires, also note depending on your cat5 cable you have the wire colors may be different also, so you need away to verify the connections too.
I'm sure someone will chime in and give a hand on wiring it up though.