Nice D, Good decision on the 700 width. I like the overflow and return. The only thing that concerns me about having the overflow and return on the same side, plus at the same height is how do you ensure the surface skim is not just the returned water? Ideally you should direct the return from the opposite side to help direct the surface muck into the overflow. Just a thought?
Return water should go out straightaway from the back, along the sides of the tank. Causing two whirlpools that looks like a figure 8. The center of the tank will flow directly back to the overflow.
Ya i've been thinking of an easier way to do this without messing with my viewing space. If you have any suggestions please let me know. I'll even email you the sketchup so someone can tweak it for me.
Might even make the overflow return bigger, from side to side. That will even ensure more that the water that return flows down the sides to create the two whirlpools.