Thank you everyone. I lost track of how many lbs of rock we bought, and we also got rock when we bought the 125. It worked out really nice because I don't believe we had to buy any more rock, once we combined the rock from the 55 with the rock that came with the 125.
the stand is quite sturdy and we did not do any further reinforcement of the stand. We live in a downstairs apartment, and all of the buildings out here have concrete foundations so we didn't have to worry about the floor. I'm not sure that it adds much if any more weight than a water bed with people on it would.
We are confident from our experience with the 55 that the tank will hold just fine. It is an Oceanic, with a tempered glass bottom. Glass is much stronger than people realize.
And yes - the rock was all purchased, even though we live in a desert, and there is a lot of rock around, it is not what I would put in my tanks.