If you really want your tanks low, at least use some styrofoam or other insulation under the tank. The
heaters will be running 24/7 just to keep up otherwise.
I had 6" between my tank top and shelf on my first rack and it's a PITA to work in the tank. 8" makes a huge difference and that's what I go by when setting up racks now. Not as big of a deal on display tanks but if you're using them for breeding or QT, you need the space to work in.
I use this pump (actually both 80 and 550):
I also use this 400gph for bucket w/c's as it sucks water from the bottom. It leaves less than a quart of water in a 5 gallon bucket.
Cheapest 3/4" ID tubing that's good quality.
For 1/2" ID tubing, HD has Everbilt in 25' lengths for $10. Do NOT use Lowes 1/2" tubing, they don't hold their shape and collapse/kink easily.
These remotes are awesome for the pumps.