I have to agree about the chocolate chip. They are notorious for eating corals and really don't do much in the tank. Also, I would scrap the sand sifter because they "sift" the sand in search of pods and worms to devour. They usually just end up disintegrating in your tank anyways.

Definitely get the coral beauty before you add any corals and get it used to eating frozen. If you add it after you have corals, it may start nipping right away.

When you say yellow goby, are you talking about clown or watchman? Any gobies you put in there of the same species should always be added at the same time because they will fight. If your thinking about clown gobies, I would advise you not to because they are bad about picking at some sps. I just had to get rid of two. The larger one started right away and the smaller one learned from the other. They killed a frag or two that I had.

The horseshoe crab it just going to plow into everything. They don't really provide much in the way of natural cleaning or whatever. The only reason to have one is to have a prehistoric animal in your aquarium.

I had a lawnmower that did great till the algae ran out. I was lucky though because he began eating the frozen stuff I was feeding. This keeps them alive, but is not good for them because its not their natural diet and their bodies can't handle it and process it properly. I would go with the suggestions by Richard.

Hope I don't seem too negative. Ultimately its up to you, but I would recommend reading up on all of the animals you ever put in your tank.