It will fit... you wont have 150 gallons of saltwater in the Display Tank though... Maybe with the sump you would.
It is all dense and displaces the water. About the hermits and snails (and more)... to start out and cycle the tank.. they might end up starving first.
I know a few others will kick in here in a few minutes with some more opinions.
I bought "the package" for my first large saltwater tank. It was awesome, tons of life and tons of extras came with that weren't advertised as part of it.
Only downside was lots of nasty hitchhikers... had to hunt out a few mantis shrimp, tons of gorilla crabs, and when I broke down the tank a year later, there was a HUGE bristle worm hiding in my sand bed.
Not likely a bristle worm. My first tank was set up with gulf rock and when I broke it down several years later it had a giant worm worm as well. Eunicid worm most likely and a BAD hitchhiker indeed.