> I was wondering what the normal "leveling up" is in math.

practice

the urge to look for reasons, patterns, symmetries, invariants..etc.

the appreciation of mathematical beauty, elegance..etc.

>but I've also taken classes in propositional, predicate and modal logic and I did some set theory

except for propositional calculus and NST which makes so much sense, most of them is controversial, ongoing or crackpot mathematics, if you can make sense of these, you should be either fine on calculus or "trapped" in a maze of settlement which is also fine.

>How hard is calculus and what comes after that compared to that shizzle?

My impression is that there are too many obstacle techniques in this area. Practice makes perfect but i don't really like calculus myself.

>What would be the minimum IQ-score for a Fields Medal?

You are a joke.