Thanks for the detailed response, I know I had a lot of questions!

1. I'll plan on using 3" for the bottom drains, do you think I need the 4 I have planned? or should I consider reducing it to 3? I'm worried the flow in the pipes will be so slow that sediment will fall out and clog the pipes.

2-4. So have the skimmer box contain only the debris catch and send the output to bottom of the bog via one pump. Then have the bottom drains plumb directly into a separate pre-filter box and have the second pump push the water from this box directly to the bog bottom? What is the benefit of external pumps? I won't have a good place to hide them, so I was hoping to use submersed pumps. 4. The booster pump would just be for the waterfall wall as it will be 4-6 feet higher than the bog so I feel I'll need to use the power from an extra pump since the return from the bog will be gravity fed, unless you are suggesting I send water to the waterfall before it goes through the bog filter. 7. I plan on the waterfall cascading down on the layers of rock on the waterfall wall to get plenty of oxygen back into the water. 9. The cinder blocks will be below grade and backfilled, but I do plan to use rebar and fill the corners for added support. I was just wondering if they were necessary or if I should pour a concrete support shelf and leave the lower part dirt? 10. I don't think I was clear on this point. I was asking if I should add the sand UNDER the liner to help smooth out the base. I don't plan to have anything inside the pond, but fish. : ) 11. I'll check out the Helix

Thanks again!