I'm not a tank main in any capacity, but I'm a big proponent of playing what you want. A lot of people say to play Paladin before playing Dark Knight, but I leveled Dark Knight first because it's what I wanted to play and I enjoy it. (They said the same thing about Astro and playing White Mage but I also didn't care lol)

But also, as someone who was terrified of Tanking (I played BLM through MSQ) it's actually not as difficult as it seems. As long as you can hold aggro, point the boss away from the group, and use mitigation tools during Tank busters, you'll be fine.