I see these snails on LPS all the time in my area. Very common. As said above, they may be an issue if they get to massive proportions, but usually they are not an issue. Just another filter feeder. There are periods where I will see a few strands and there are weeks/months were I won't. It's up to you what you really want to do with them at this point.
The small starfish that is practically all tentacles is probably a type of brittle star, but a pic would help if you really want to know. If a brittle, they are harmless and helpful.
The dip will usually make things jump ship. I can take a coral from someones system or from a LFS and dip it and things I couldn't see on the coral come flying off of it. Double check next time the ratio on your particular dip. What kind are you using?