You should ask them for the actual name of that species, they're using a common name and an incomplete scientific name. Without knowing the actual species (because "ghost lobster" is often used to describe a lot of crays) you can't be sure what the requirements are going to really be. I'm not sure if that site is any good or not, I've never dealt with them, but they're using some copy & pasted information... which is more reason to know the actual species and look up the necessary requirements. In general though, a cray that size should be fine in a 46 gal but if you're getting more than one... then you'll need a much bigger tank. And it will more than likely eat your shrimp, a lot of species of crays are really fond of shrimp.