The things on the left look like hydroids, although it's hard to tell.
Cone snail. Get rid of it, very venomous.
It is not possible identify a snail from such a vague text description. There are a number of other groups of snails having similar descriptions, including several completely innocuous ones. A picture is really a requirement here to make any sort of serious guess at the ID. While I can't say that a cone snail is a complete impossibility, I will say that those snails are so incredibly rare as hitchhikers that I have never actually heard of anybody ending up with one since I have been in the hobby. Therefore, I would find it quite incredible if that is what this snail is. It is far more likely to be something like an olive snail (Olividae) or even some types of whelks like in the Busycon genus.
EDIT: missed a post.
So are coral shrimp good predators for bristle worms. Call them what you will but I have seen them eating my polyps and have been un able to catch them before they retreat. I saw one that was at least 8 inches long.
Yes and no. Really big bristleworms are immune to most common animals except for quite large hermits that will possibly be more destructive than the worm just from clumsiness (like Dardanus megistos). The best approach for removal is usually to lure out the big ones with bait and manually remove them with tongs, while having something like a CBS or other medium-sized Crustacean to control the smaller worms. I have used both small and large Stenopus species for bristleworm control in tanks. They don't often catch the worms they chase, but restricting access to food is a big part of the battle to keep worm populations under control - and coral banded shrimp are most active at night when the worms are also most likely to come out.
Do be cautious about blaming the worm. While it is possible for them to go after perfectly healthy corals (I have seen it), it usually only happens when the worms experience a population boom and then are starved. More commonly worms will go after decaying organisms, and it's not always clearly visible when coral tissue starts to go south. Another possibility is that you have something like a Hermodice worm instead of one of the other, much more common species of spiny/fluffy-looking bristleworms. It would be impossible to tell without a good picture.
Top middle of this photo there is a an oyster of sorts with polyps on the top of it, anyone seen it before? I'm hardpressed to find any info on it and should I be feeding it?
I can't make it out from the picture. It is a common thing to see though and there are several types that show up. Often they are pretty hard to keep alive unless you throw a lot of filter feeder food at the tank; target feeding usually fails. Usually the tank either has enough food for it or it doesn't, and adding sufficient supplements can give you water quality problems pretty fast. It's not so bad if you've got a bajillion filter feeding things to feed, but with just one little clam a lot is going to go to waste.