In a 10 gallon you aren't going to have many options; that's simply too small. The cray alone would prob be fine in there for awhile but even that's going to end up a bit tight for him. The general rule of thumb with tank mates for crays is (1) don't get anything the crayfish can grab (nothing too small and nothing extremely slow), and (2) don't get anything that will harass/attack your crayfish (NO cichlids). My advice, splurge for a 55 gallon or so, they aren't that big, expensive, or difficult to maintain. And it allows you to throw in a plecco or 2, and I like sharks as tank mates. Balas, a red fin, roselines, etc. I've actually had mine with a black ghost knife and rope fish as well. I think that gives you a pretty good variety for options, but make sure he has a place to hide and feel safe, when they molt they're extremely vulnerable to attack even at a massive size.