Since I am just starting a new reef tank, I'll tell you what I was told. You can draw your own conclusions:
"Crabs and snails are a waste of money! Crabs will eat the snails and the snail hardly eat enough algae to justify their cost and their constant demise by the crabs, which after a while get used to eating snails only and so will starve after all the snail are gone. That is until you cough up some more money for a new set of snails." TRUE?? I DON'T KNOW!!!
"Buy a few tangs depending on your tank size, a couple of nudibranch, and a few sand stars and cucumbers. They will take car of the debri in the sand and the coral on the rock for the most part. The glass will be left for you. You also ahve to feed the tangs properly with other nice food like nori, shrimp, octopus, etc.." TRUE?? I DON'T KNOW!!
I can tell you what I do know though. I saw this guy's tanks in his shop and his personal tanks at home and they are awesome. They have more than half the lighting most people in this board has and have tons of SPS and clams thriving even in the poorest lit tanks, has more fish in each tank that is packed with corals than I ahve ever seen in any tank, and everything is doing great for the past 20+ years.
This is a long way of saying to look around and listen to what other people is doing.
I personally plan to add the cured live rock and live sand, 3-4 tangs, and the other above mentioned critters after 1-2 weeks.
Good luck finding consistant answers in this hobby.