Converting my 20 gallon over to a 25 tall

[GoneReefing]

Here's the deal:

I got this 25gal tall (24L x 12W x 20H) for christmas. (My wife doesn't like the current 20 due to being a hand-me-down and she wants a nice clean setup like my 75 in the back, just lights and tank, no skimmer to be seen, heater, etc)

So the plan is to drop the current 20 gallon inhabitants and equipment into the 25 and place the 20g as the sump.

I am working on building a stand to hold the 20g as the sump and the 25g as the display.

I have a spare return pump that is rated to roughly 700gph, but I know with head loss it will be less than that.

So finally here my question:

Will that pump be enough to do dual returns? I was thinking about drilling two holes with a nice size overflow box ( >=12" <= 24" in length).

My current pumps for circulation are 2 koralia nanos and I guess the return from the bakpak.

I want to add the dual returns for extra flow and was even thinking of putting a swcd on the return to make it a little more random.