Looking really good
Did you get the hermits & snails from Abyss? How much did they set you back?
The large hermit is a Electric Blue (Calcinus elegans) they attack, kill and eat other snails/crabs so just keep an eye on him. The red on the sand looks like cyanobacteria to me.
When they shed their skin they tend to hide for a few days to a week so to give the new skin time to harden. They shed when the change shells or at least mine do. I would leave to old skin in something will feast on it. The more empty shells you provide the less chance a hermit will take one from a snail.