Want some crap? Heck, I'm full of it
. Seriously, though, you have listed some corals which can thrive in a tank that size with that lighting (I have that same exact light on my 12g). None of them can be touched by any of your soft corals, though, so make sure if you try them to give them plenty of clearance from where your softies could reach at their biggest & fullest expansion.
IMO candy canes are the easiest & least expensive of all the ones you listed. Also, because of their stony, branched skeleton it is easy to affix them on your reef with enough clearance that softies below can't sting them. Their skeleton also makes it extremely easy to frag for trades. If you feed them at least once a week with a tiny piece of meaty fresh seafood (mysis shrimp, squid meat, prawns scallops or salad shrimp) they will show better polyp expansion and faster growth. Just make sure the piece of food isn't too large - they will take bigger pieces in, but throw them up in a few hours mostly undigested and be at an actual energy deficit then. Aim for pieces like about the size of this lower case letter - o -.
Acans are a great one for a beginner - but don't go with an Echinata unless you can keep it at least 8" away from all other corals on all sides because this one is extremely aggressive. But a Lord (don't go for non-indo unless you are keeping your system at a lower temp & salinity than commonly seen) is a good and hardy coral which as long as it is fed on occasion will grow well for you. The price of the Indo lords has come down quite a bit since I was first bitten by the 'acan bug'. I feed mine about 3x a week.
Open brains are nice. They are hardy, eager feeders, and their sweeper tentacles aren't too long. I had one in my mixed 55g and I really miss it. But it got just too big to put in my 12g, so you have to weigh the size they will grow to against your desire for alot of variety in your tank. It won't be easy to frag like these others, so if it gets too large you may have to part with it.
Plate corals are hardy (short tentacle - long tentacle has proven a challenge to most), cheap, and cool. They move along your tank bottom. You can't keep them on your rocks because they will move off of them and fall into other things getting stung or damaged. However, if you have softies on your sand bed I wouldn't put a plate down there because they will end up touching leading to injury or death. Also, if you have gobies which spit sand this will irritate your plate and it will not do very well. I also recommend feeding these guys at least once a week.
Blastomussa can be kept in a tank like yours. But you have to be comitted to spot feeding it at least 3 times a week, and for best polyp expansion I feed mine daily. You will have to use the same types and size of food I described for the candy cane, turn off your pumps, place on top of the mouths of the blasto & stand guard so other inhabitants don't steal the food. Blastos are a little slower eater, so wait until the food is swallowed to turn the pumps back on & relax your guard. Keep in lower water flow areas with moderate light. Don't get a wild one, get a captive propagated one. They're just too fussy while they're adapting to our artificial environments.
I can't comment on a chalice as I have never kept one. I know some have very aggressive sweeper tentacles and others not so aggressive. It is a coral I want to try when I set up my larger system - I hope some experienced chalice keepers can chime in with some good advice on them.
Whatever you end up trying, none of them should be manhandled on their fleshy polyps. If you have any shipped to you ask the seller to attach them to a piece of floating styrofoam in the bag to minimize irritation & injury from the bag itself. And post some pics!
