While I think all the advice that's been given is great (and very similar to the advice I recieved when I started playing around with tanking not long ago) I think it's important to consider some of what you've said in terms of endgame.

To reach max level and the current 'end' to the main story there are definitely dozens of dungeons you'll need to group up for to complete and in the interest of making it easier on yourself I would definitely stay on top of your enmity generating moves and defensive cooldowns. That is a smaller chunk of your kit to manage and I know personally as a healer I don't care too much about my tank's damage output as long as he is keeping enemies on him and using some mitigation if he decides to pull big. There are a lot of great tanking guides out there you can skim but with your current background for this I just don't want you to get bogged down in the tank DPS meta and get discouraged. Damage can come later.

I just don't want you to have an unrealistic outlook on what is between you and the current endgame, there are definitely a lot of forced dungeon participation quests in the main story.

Sucks that you're on Ragnarok, if you were on the Aether data center I'd run your dungeons with you.