So i would recommend (and from memory I think @overeasy recommends as well) is a raspberry Pi power supply for the 5v supply, and yes the Jaycar power supply for the voltage reference will work good. Personally I use the raspberry pi supply and the Doss adapter from radio parts and these have been running in a warm meter box for 12 months now.
The Doss supply and the raspberry pi supply sit side by side ok with 2 din rail GPO’s with a 1 din space between. Don’t know about the Jaycar physical size though.
The din rail GPO’s are normally 2Din size, you have 5 spare din size on you bottom row so place a 1 din space between then.
As Giraffe said, most distributors reserve their panel area for their equipment, so best bet would be mount it on the metal panel under the circuit breakers.
Photos of mine is here. I’ve placed my Iotawatt on the reserved area, however we have remote meter reads in Victoria so never a meter reader visit, but an inspector I know doesn’t have an issue with placing items like this on the reserved area, just don’t use screws. I’ve used industrial double sided adhesive.