The false bottom may be the biggest concern with making it a planted tank.
If you could post a pic that shows the false bottom, or put up some sort of diagram, it would help to get a better understanding of what you are working with.
I've heard concerns about having substrate too deep, but I'm not too familiar with the potential problems.
If the false bottom is removable , that might be the easiest thing. Otherwise, possibly filling it with something like great stuff foam.
I don't know what the bit about crushed coral is, unless the person who suggested it was thinking of using the false bottom as a sort of under-gravel filter for a marine set-up?