I wish I had enough time to answer your questions in detail. But I'm off to a meeting. if no one else jumps in I can fill in some blanks.

1. Largest sump possible that will fit under your tank, and if it were larger than your display, that would be good too. But most don't.

2. pump up, never down. The overflow will bring the water back down to the bottom.

where do you live, you should stop by one of our places to pick our brains a bit before you go too far down a rabbits hole. If you're up in the stoneoak area or bulverde, I would gladly open my home to a visit.