Interesting I love to see mods. That would be a interesting one indeed with 3 on one heatsink. Don't think I've seen anyone do it.
Are you going to use Y adapters or what is plan to get power/data over to the compacs?
Ideally, I'd like to put 3 sticks on each side of the heatsink (stick|heatsink|stick), and with the Y cables it's going to be just fine, I can even put the USB doctors back to back. (hopefully the display will face out, not in)
I received my 10 ports USB 2 hub today, it's likely to be limited to 500mA/ports, but if it's not it has a 12V/5A power supply, so it's quite good (better than my 12V/3A usb3)
anyway, I'm waiting to get the USB doctor delivered, and then I'll get started after the grouped-solo pool run.