Scorpions are awesome. I have an emperor in a 20 gallon too (I had the same situation -- empty tank with nothing to put in it). All he needed was substrate (I use coconut coir), a couple places for him to hide, a water dish, and a heating pad to make sure he stays in the mid 80s since they like it warm. The only real maintenance I have to do is spritz his substrate. Mine isn't a picky eater and tends to eat whatever insects I give him.