For which pump to get the reef life support systems DC pumps look real pimp, low power draw and controlable flow but are only internal pumps, check them out -
http://www.rlss.ca/#!dc-pump/vstc3=dc10000
I don't have one those pumps but I plan on picking up the DC5000 for my 90g tank real soon.
Plumbing is a pain, your taking the correct steps by laying everything out, it'll save you lots of trips to the hardware store that's for sure.
I would also consider increasing the volume of water in your sump area, for me mainly I would much rather replace water from the sump then from the display during a routine water change, plus as mentioned before you can have more rock in the sump then in the display tank so maintenance of sand will become easier.