Sump design...

I want to add a sump to my 48G Bowfront for the two primary reasons listed
below. I do not plan to make this a refugum at this time (like the Marc
Levinson has ones on melevsreef.com). I will place the heater, skimmer,
H.O.T. wet/dry filter and canister filter in this sump. The Sump will be
about 10 feet from the tank. Please assist me in getting this done
correctly. The tank is not pre-drilled and does not have an built in
overflow. I prefer to use an external one as you will see below.

Goals
1) Increase the total water volume - to allow for more Fish (I have 100Lbs
live rock and a few corals now)
2) Hide the heater, power-heads, skimmer, and move about 50Lbs of live rock
from display tank to here etc....

Items I am looking to buy:
-all the required PVC and aquarium safe cement
-1 x 40-55G glass tank for sump from LFS
-1 x overflow (rated 600GPH)
http://www.drsfostersmith.com/produc...1&N=2004&Nty=1
with all of the sponge, lifter pump, and filter
-1 x Switching Current Water Director (SCWD) thanks to www.melevsreef.com
http://www.drsfostersmith.com/produc...&N=2004+113782
-1 x Pump - the Sump will be about 10 feet from the tank. How do I
calculate return rates and overflow rates? I am looking at the pumps below,
are they too strong? Do I go with lower GPH?
-----either QuietOne Model 4000 (1000Gph) -
http://www.drsfostersmith.com/produc...&N=2004+113041
-----or Mag Drive Pump 1200 (1200Gph) -
http://www.drsfostersmith.com/Produc...13041+1 13565

Am I missing anything?

Thanks for your help!