I'd wait at least 6 months before adding a sea star. They require very good water conditions to survive long term and are very sensitive to changes in temp/ph/sg
. I wouldn't get more then 1 sea star for a 55 gal
and only get the Brittle Star
which is reef safe. A long 3 hour drip acclimation is best for sea stars before adding to the tank.
Personally I wouldn't add more then 20 hermits or snails to a 55 gal
even after it matures. Usually unless you have a ton of lr
there isn't enough food to support more then that.
I haven't seen any difference between blue or red leg hermits. The blue leg hermits are prettier IMO
but are not any better at scavenging then the red leg hermits.
I'd hold off on any crabs for a couple of months to let your tank mature more. The ones you mentioned are also considered "reef safe" but I'd limit your tank to just one crab.