I just thought I'd post an update, for all those following the project.
Since creating the first round of PCBs, the PocketQube form factor - PQ60, underwent a few changes. These changes included the PCB size, the hole location and diameters, and the backplane connector pinout.
So rather than push on with the original layout, I decided to update QubeCast Max to match the PQ60 version 1.0 specification, as well as update the Arduino Pro mini adapter board. These are both a work in progress, but it has meant that I've needed to change the SMA connector to a UFL connector, amongst other things.
I also had concerns about powering the board sufficiently. I'm going with 2 approaches for this.
1. Use an additional breakout board connected to the stack to power both the radio and the Arduino
2. I found a version of the Arduino Pro Mini that has an LM1117 LDO with 800mA output
Option 1 is possible because I've created a breakout board, called ProtoQube! I'm even selling it on Tindie. This will let me plug in a breadboard power adapter straight into the power bus of the stack, which will let me run everything.
Option 2 will need a slightly different arduino adapter, because it seems to be different to the regular Pro Mini, plus they haven't arrived from China yet!
I'll post more once I've finalised designs etc