Help me design my sump!

Saltwater or freshwater? Here's the design that I used for my 20 gal sump. I based it on the Aqueon Proflex sump:

make a huge moving media filter.

here's mine.

That's alot of real estate. I wish I had that much room under my tank. Just a few ideas that rolled off my head... There's enough room there where you could build a freshwater refugium (good place to nursery plants or keep feeders): Inlet -> mechanical -> bio chamber -> refugium -> return
Or you have lots of room where you could make a 2-stage mechanical and have super polished water: Inlet -> 100 micron mech filter -> bio chamber -> 50 micron mechanical -> return
The possibilities are endless here.

I'd probably look at both posted designs closely (although Gill's is closer to your size) and then add plants to the top of the aquarium. See this whole thread http://www.monsterfishkeepers.com/f...4763-Cheap-plants-less-nitrate!-POTHOS/page79

I think that would give you a stable and easy to maintain system for 1) mechanical 2) biological and 3) nitrate removal. I think a 40 gallon might be a bit to the smallish size for a 260 if you take up space for a refugium. Also, I think you'll need to jimmy up some lighting if you do that. The good news is you don't have to do that as the plants will work very well on top of the tank and they don't require any special lighting. (Ambient room light works fine.)

The sump can go under the tank and be enclosed to reduce evaporation and you won't have to insert lights for plants there.

Just a thought! I like the idea though of a sump though and you are exactly in the right place to get advice.

That sounds great! Be sure to post some pics when you get it done. I don't have much experience with K1s. I'd really beinterested so see how it turns out for you.