Haven't seen it but for the rock you need just about double the gallons in the tank for LR
do just go out and buy about 100-120 pounds and I know your on a budget but this one you should try to pay or the best you can get because this is the basis of the tank filtration of nitrates so I'm guessing it will be around $150-200 range it's a little expensive but it helps the tank a lot! As for the tang it's possible but don't add him until your clownfish and any other are in the tank so the tang isn't as aggressive. But it's up to you I would not think of putting a tang in a tank under 100 gal
. If would suggest that you get the following. A dwarf angle fish ( one of my favorites very very colorful) 2 clowns ( really easy to care for) and if you start to notice hair algae which is probably always no matter what is going to get into our tank for that I suggest on of the three a law mower blenny ( although sometimes you can get one that doesn't eat it at all) a sea hare (slug) haven't tried this one yet but I hear they are the elephants of the sea the eat and s$@t a ton and will eat all the hair algae until there is no food left and if it doesn't grow back then it will die
also a emerald crab again 50 50 it will eat the algae again hope I helped!