Freshie maybe going salt with my 300 gallon?

[Hustler]

Thanks guys she is my baby
As for the arowanas and fighting... I a hit and miss. had a super red almost beatn to death a few times so its how many fights you can handle before you break them of the mean streak
As far as livestock its not going to be that drastic of a switch from 2k tigrinus cats, asian arowanas, sting rays ect it seems most salt fish that catch my eye are pretty affordable..... but the corals and rock are a bit daunting.
for a 300 gallon i need 150lbs of rock plus live sand correct? Can I add rock in say a second sump thats all plumbed in aswell to keep the water flow in the tank from being obstructed?
Im a little worried as Ive seen live rock in bins for sale private that may or may not be dead and I have no clue what im looking for as far as quality rock other than its shape?
Im trying to find a good starter walkthrough for my type of setup but they all seem to be for small sized tanks and dont really get into larger applications.... Like the old inch per fish rule the stores used to quote.... Goes out the window when half your fish are over 2 feet LOL then its how many GPH your pushing salt must have a few of those rule of thumbs that are in the grey area as well?