not a bad idea, if I may make a suggestion: Instead of of copying xiii's atb system, you could allow the stamina bar to grow every few levels, giving you more stamina to use in fights. I'm not so sure that the battle UI would work, since ffxiv is has both controller and keyboard controls (I'm a keyboard user for example) In some ways the stamina cost in the current interface is like the slots you are talking about, and was probably what the developers intended.