Not to give away the secret sauce but, I would recommend you make one RPi3, get diamondd running... copy the image... and split the coins between the two Pi's. I switched out of RPi because it did not have coin control, solved it by making more than one pi3. There is a sweet spot to how many coins each Pi should have.
Not sure I understand correctly, but what do you mean with "it did not have coin control"? As far as I'm aware you can use setstakesplitthreshold to control the coin pile size for staking. This is a RPC command, so it works with the QT wallet, but also with the headless daemon on RPi.
i think he is talking about use a GUI wallet on a raspi instead headless
and use the coincontroll gui (options wallet enable coincontroll) for which there is no similar replacement in headless wallets
and there i agree a gui wallet should not be used on smaller raspi then the 1 GB ram ones
ideal are 2 GB ram boards
I agree 100%.
This board looks promising, it's supposed to ship in early 2018.
https://www.indiegogo.com/projects/renegade-arm-computer-with-usb-3-on-android-linux#/
It has DDR4 and much higher IO, which the PI lacks.