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.