Okay, mantis are pretty easy and were the first thing I ever kept was a peacock. For smaller mantis a 20 gallon is fine. Just hook it up with some LR, larger pieces and some rubble for it to build with. I fed mine a piece of shrimp or squid once a day and maybe some krill here and there. I also put in a few emerald crabs and snails so it would hunt. They can lose their dactyls during a molt if they don't use em. Water quality is the same for most fish and inverts. Nothing fancy. 0 ammonia, 0 nitrites, 50 or less nitrates and a ph between 8.0 and 8.4 should do fine. Now post some pics when you get it togther.