I wouldn't run any sand or rubble rock. I personally like keeping things as simple as possible. Keep in mind you will eventually have to clean, rinse whatever you put in there to keep from trapping nutrients. If it were my fuge I wouldn't even keep macros. I don't like doing maintenence on them. I would go bare bottom everything so any detritus can be siphoned up. Even in the tank go bare bottom, just run a sweeper(power heads on the bottom) so it all flows down to the fuge for easy water changes. I would just make sure I had room for a monster skimmer plus 2-3 reactors for bio pellets, carbon, gfo or whatever, even calcium reactor if your tank is too big to dose. It's really all personal preference though.