Hello, looking to get as much info as I can

I hope I didn't make a bad buy. But I also bout that live rock and there were too emerald crabs attached that I didn't know about, they have been in there for almost two days and seem to be just fine. Is this rare? Or is it a good sign meaning that my water is in good condition?
The Emerald crabs are good, they're algae eaters and you got about $10 worth of crabs free. Keep up with water changes to keep the nitrates and phosphates down while the tank's cycling. Personally, I'd add a little more rock in there, maybe a smaller flat piece for the bottom for lower light corals. The neat thing about these small reef tanks is if you do a 5 gallon change every 5 days, you've effectively done a 100% water change over the course of a month. If the nitrates start climbing rapidly, do more water changes.
Cool thanks again rob, I was already thinking f putting more rock in there somewhere but as of now my LFS is kinda limited on rock until they get a new shipment in. But I will definitely look for a nice flat piece for some bottom corals. And check this out I came home from work yesterday to wha looks like a nice brown algae bloom all over my sand and rock and its only been 4 days.
Hey anyone know what this guy is? Found him in my tank the other day. Its definitely a little snail but is he good? Bad? I dunno if I should worry about him.
Cool thanks, so no worries about this guy? And how is he surviving if my tank is just a week old? Enough bacteria for him to eat?