Average of all your gear. Its whats used at lv cap to continue progression. if youve ever played Destiny, ilv is your Light lv. Lv 50 gear caps at around ilv 130 and lv 60 gear caps at 270.
ilv doesnt really come into play until youve reached a lv cap (50 for ARR stuff, 60 for HW, etc...) so I wouldnt worry about it right now if I were you. Also as a heads up if youre away from the game, you can check your ilv for the class you logged of as on
lodestone.
Theres no built in voice chat in game. Think most places use discord for it, theres apps for it on the app stores. If youre in the Ultros GAF fc, the message that pops on when you log in has our discord link.