Jeremy,
Does this get shipped to your door or have to pick up at airport?
We can either ship directly to your door via UPS, or to your airport, whichever is easier for you. We also sell our rock by net weight, not gross weight. This means that if you order 40lbs of rock, you will receive a box that weighs in the 45 - 47lbs range. We do not charge rock weight price for packaging materials. A lot of places you order 40lbs of rock from you will receive 34-36lbs, while the other weights is packaging material.
I would do somewhere in the 55lb - 65lb range. That should allow you to keep a really open aquascape, and not fill the tank up very high. We can also pull the rock, and if we feel like it's starting to add up to more than what you're looking for we can always adjust the order to remove some.