For a single module a 2.5A 12V wallwart will suffice.
Power Stacking will possible through high current screw terminals or 6Pin VGA Bridge cables (not decided yet).
That way 3-4 Modules could be powered through one 6 Pin VGA Connector.
I would like to suggest that in addition to a barrel jack and 6-pin PCI-e Mini-Fit Jr power connector, that the board also have connectors to accept 12V power from a 4-pin Molex, and also from a SATA-style power connector.
Heck, add in some screw terminals too.
Also, an on-board header to power a fan would be a nice touch. Software-controlled fanspeed would be even nicer.
I'm not sure what the part cost is but it might be cheaper across the runs to support one interface and use adapters for odd-ball combinations. 4-pin Molex would work well combined with some 6-pin PCIe to Molex adapters.