Sensitivity/gameplay tips needed

Hello. First of all, I'm pretty "new"(got around 150 of 180 hours but still feeling like a noon) to this game(it's the first FPS I started playing for real).

One of issues I'm having rn is finding good in game sensitivity and mouse polling. I either end up with too high sensitivity or too low(which makes controlling recoil pretty much impossible) and mouse pooling rates(refresh rate?) also have huge impact on current sensitivity so honestly I'm struggling to find anything that would feel right.

Second thing is, are there some good channels or people on Twitch I should watch to improve myself? I ranked up recently to Gold IV and it feels like completely different game. People peek very aggressively, spawn killing happens a lot, strats, operator picks and strategies are very much different compared to previous ranks so I'm feeling like a child in fog. Other people aim and reactions times are beyond light speed and laser like precision.

Any help and tips are appreciated. Thanks.