No such thing as a reef safe lobsters, you may get lucky but its not a chance worth taking for something you will never see. Also in a 20 gallon you should have 3-4 fish max. I would also tone down the coral (it does grow) I’m not looking at your numbers right now but I think I saw somewhere around 20 corals. I have 15 or so in a 75 and I’m running out of room. You could add a few more snails and hermits. I would also limit cleaner shrimp to 2, 3 max. Overall you have to tone it way down or get a bigger tank. Look into a anemone crab they are awesome to watch, they stay small and in sight, and feed from the water column. Or a boxer (pom pom) crab they are safe small and very cool. Just my advice...