Profession (Fortuneteller) is a skill; strictly speaking that's pretty much just for earning gold during downtime but it's certainly something you can do. And nothing is stopping you from simply taking Divination-school spells and fluffing the act of casting them as using the tarot. There's even a
feat that you can take to make your divinations better by using a deck of cards as a focus. You might also look at the
Cartomancer archetype and see if it suits you.
Cauldron does cost you a hex slot, but it gets you Brew Potion two levels before most casters would even qualify for that feat, and you'll get another hex at every even level anyway (plus you can take more with the Extra Hex feat). You'll just have to decide whether your character is more combat-oriented or support-oriented for their first level.
If you want more specific or in-depth advice, I'd recommend checking out a forum more oriented around character optimization, such as the
Playground. But the point is there are tons of ways, even with third-party materials off the table, to build a character of any class in this game.