The LDD-700H and LDD-700HW have a different in mounting styles. The LDD-700H is designed to be mounted on one of our boards, the LDD-700HW has wires so you can connect it to a non LDD board.
Yes you can put each lumia on 6" heatsink as long as there is a fan running
Yes, you can put the lumias in series and control 5 channels.
I would suggest getting the 200w meanwell power supply we have (much nicer unit).
Also you want to change your LDDs to the HW versions if you arent using one of our boards.