How do you tell which level your Limit Break is at? All I've noticed is whether the icon is available or grayed out.
Does using a Limit Break prevent anyone else in the party from doing so until it refills, or can everybody do their own separate Limit Break?
The limit break bar shows up in your UI customisation option thru the menu - top-left of your screen iirc (on the PC, at any rate). The hotbar ability is found in with the rest of your general actions in the ability pane (P by default on PC). In a "normal" party (light party in game), you can fill up 1 bar (grey = empty, blue = filling, orange = full) throughout the instance, with the final boss (at least, for the first 3 dungeons) allowing you to fill a 2nd bar. When someone in the group pops it, it empties for all, but only uses the full bars for calculations. So 1 bar = level 1 LB, 1.8 bars = level 1 LB, 2 bars = level 2 LB. So essentially, use it as soon as it fills (if that's the plan, prob not a good idea if you're in a DF pug), or wait, save for last boss, build up 2 bars and then a) get THM/ARC to use it if you need AoE spike to clear adds, or b) get LNC/PGL to use it on boss for a big chunk 'o damage.