Nitrates below 40ppm is fine for FOWLR
. You want to get below 5 for a reef tank. You can reduce nitrate with partial water changes a/o macro algea a/o dsb
a/o a denitrator.
As for a cleaning crew, you should start with a small crew of snails (nasarius, cerith, astria) and add more as you build your livestock. You may also want to add a bittle star fish (I have 2).
Astrea Snail-most common of all saltwater tank snails. They are excellent algae eaters and will forage all over the rock, sand, and glass. These guys fall very easily and can not right themselves up and die easily.
Cerith Snails (Cortez) - Good algae and detritus eaters that forage rock, glass, and sand. Some can pick themselves up and some cant.
Cerith Snails (White)- Good algae and detritus eaters that seem to stay in the sand more than the cortez, but can be found on the rock and glass. Once again, some can pick themselves up and others cant. These guys are good sand bed snails to shift the substrate around.
Fighting Conch Snails - These guys are all about the sand bed and are very cool to watch. They usually dont get flipped over, but if they do, they can kick around and turn themselves back upright. They very hardy too. Get one per 2 sq. feet of tank is what was recommened to me. They tend to disappear behind the rocks for a few days then come back around to the front again.
Mexican Turbo Snails - super fast grazer that will knock out some algae in no time. They mostly stay on rocks and glass, but will work the top of the sandbed too. These may be cold water snails that dont do so well in a reef. But, once they are adjusted... they seem to be very hardy and active. Mine are going on two years and are huge now. I originally got them for a hair algae problem. They do tend to knock over anything that is not glued in place (corals, clams, rocks, etc.) Well I just ahd one knock a coral off the the plug it was glued to, so they can knock over just about anythng.
Nassarius Snails - They mostly stay in the sand, but will sometimes make short trips up the glass. They are mainly detritus eaters and do an excellent job cleaning and shifting the sand. I think these are also some of the most hardy snails out there. These guys can flip themselves upright very easily and quickly. They are fun to watch as they come bursting out of the sand bed at feeding time.
Nerite Snails - Mostly a rock and glass snail that are all about the algae. The dont move very fast but the areas they have been in are clean as a bell. These guys like to crawl outta the water some. These are great snails, but also have trouble turning themselves back over. Mine usually end up in the sump where they can get above the water line and come back down when they want to.