Hm, I like the idea of the the external overflow box keeping plumbing out of the tank, but really don't like the thought of a box full of water, made of glass, with the only mechanical bond being the caulking. Now that I have the extra room in the tank, we'll just go with the internal overflow as planned.
Also read a bit more on surface skimming, seems like it definitely could help with water clarity, aside from what Diana mentioned about floating plants being a minor downside.
I am figuring there could be up to 70-75 gallons of water at one time, so will be going with 1.25" drain plumbing. That should be able to flow around 1000GPH, well past the 700-800GPH I'll need for 10x turnover, with some to spare. 1" flows 600GPH (http://saltwater.aquaticcommunity.co...umbing-basics/
) which is not enough. I've also read that 2x capacity for the drain is ideal, but with the BeanAnimal setup I shouldn't need to oversize that much.
Return plumbing design is next up, the pumps' combined lowest GPH rating is 760GPH, assuming that means with their intake adjusted all-the-way-closed to all-the-way-open? The other numbers combined is ~1200GPH. At any rate, the highest they should have to pump is 3-3.5', so 1200GPH minus losses (300GPH for height, 120GPH for two 90 elbows, 100GPH for check valves) brings it to around 750GPH, which is just about right (and I am being somewhat conservative with those loss estimates).
Also, some SketchUp sump diagrams coming soon...