Congrats in getting it!

Quick lil tip, I'd totally suggest picking miner and woodcutter early since you can do those challenges casually as you're traveling through the game.
You can switch classes whenever you want, so don't think that you're stuck to one class from the start. It's fun to change them up. I've tried all of them besides hunter and paladin. You can skip the intro quest after you do the first one, though, I would suggest you do one from each of the three categories of classes -- combat, gathering, crafting.
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TO ADD: Classes for each category
- Combat: Paladin, Mercenary, Hunter, Wizard
- Crafting: Carpenter, Blacksmith, Cook, Tailor, Alchemist
- Gathering: Miner, Woodcutter, Angler
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I would also suggest that if you do the angler class, don't skip the tutorial quest. I sorta regret doing that since I had to later learn it from trial and error. Luckily for me, the way you fish reminded me of how it was done in Okami, as there was also a bar, so that wasn't so bad.
While you can do challenges while you're different classes, there will be challenges that are Life-specific ones so you HAVE to be that class for it to count. And you have to be that class to turn it into your Life Master.