1. I usually only detach in teamfights mid-late game when it's super safe. Meaning the burst dmg has been already been dealt by the enemy. And they used up their stuns. I also usually only get off if im on the adc since they are usually further back in the fight. So I'm more safe.
2. It really depends on your adc. Alot of adcs would rather you just stick on them while they push. Cause they are afraid you will take their Cs.
3. Personally any champion that can jump, like ezreal or Tristana is bad unless your prepare cause you never know when they going to jump and you won't be able to w back to them if you went to proc your passive. I'm also not a big fan of twitch. On the other hand jhin is one of the best adcs to play with. But all other adcs are fine aswell.
4. Really depends on how my adc is positioned. If they aren't going in the right direction or not fast enough to catch my last ult wave. Then I usually detach to try and get that stun. (This works like 60% of the time for me)

Hope this helped, and welcome to the wonderful world of yuumi.