learn efficient EOLine and ZZ blockbuilding
just slow solving and taking time to plan out the EOLine does a large amount of wonders to improving your times with ZZ
1. Aside from the UR-case and similar, i think i don't i really grasp the concept of fingertricks. As my favorite alg is the y-permutation i'm able to do just sub-4, someone on youtube was able to do the same alg reaaaly fast. How is this possible?
practice, depending your algorithm using a better one than what you currently use (duno why you love the y-perm i hate those and learned COLL if only for the single reason of never having to do one ever again)
2a. Should i cube more to cube faster or should i learn to solve efficiently and try to incorporate it into my cubing style?
slow solving for efficiency and lower movecounts
2b. I heard a good cross should be done in 7 moves. If i want to cube efficiently, what would be the goal of each zz phase?
EOL in under 10 moves, F2L in around 30-40, LL whatever that's usually fast enough anyway
3. Are there any wrong/sloppy habits i could have, while i'm not aware of them? (probably as a result of me doing cubing as a 'casual' hobby the past two years)
wouldn't know unless you posted a video or something, hard to comment on something i don't see.
also since oyu say you're a ZZ solver, there is also a thread in constructive speedcubing for ZZ, you can go check that place out as well.
best of luck to you