1: you can also turn it on when you queue for a dungeon/trial/raid, but only if it's the same level as your job, i.e. if you have Tank Stance on as a level 70 and queue for Ala Mhigo, you will still have it on when you enter.
2: while shirk can be used to troll/grief, it's mainly used for Tankswap mechanics, like a tankbuster that gives a vulnerability debuff of some sort to prevent solo tanking.
3: depends on the dungeon and your party members. Some dungeons, like Bardam's Mettle, hit harder than you think, and not every healer can handle full pulls in places like that. It's acceptable to pull it all in level 50, 60, 70, or 80 dunegons, because they have a more lax ilvl sync than other dungeons.
4: using them ain't enough. You need to ROTATE your defensive cooldowns, rather than using them all at once. That way, you can survive more attacks for far longer.
5: you should mention to use full combos, both single-target and AoE, depending on the amount of enemies youre tanking, as you generate more emnity by using full combos than random attacks.
6: you can use an invuln when you absolutely need to, especially if you're GLD/PLD, or a lvl 76+ WAR with NF for massive recovery.
7: they are when you're in an invuln state, or during certain mechanics that require you to get hit, like in the Lyon duels in Bozja.
8: your "captain obvious basic guide to DPS" says otherwise. Unless you mean when dealing with attacks that cleave, in which case, you should've mention that in the first place.