Welcome ttb!
First of all, after reading so much whining and complaining about this game, it is really nice to see some kind words for a change. Maybe i'm too much of a fanboy but i can only agree that the immersion this game creates is unrivaled so far.
I am by far no expert in this game but i'm trying to help as best as i can.
1. I think it is not recommended to use the negative tank for anything else than emergency dive. Due to the fact that it is really hard to stabilize the boat once you reached the desired depth plus you have to use a lot of precious compressed air to blow it out again.
However: It has proven to be a very good tactic to stay hidden during an attack once the torpedos hit, to not start the engines but instead use a little bit of the negative to get down to safety depth on the spot. Destroyers hate this trick
2. I think it is more historically correct to dive very slowly and carefully because of the foam that faster speeds create on the surface. Although not visible in the game (yet) due to the game not having the best graphics i think it is still modeled to some point. Example: Going fast and sticking your periscope out makes you very detectable compared to slower speeds so even if you don't see the splash and foam effects, pretend they are there and act accordingly. Emergency diving of course does not count. Then you should go down as fast as possible.
3. Struggling with destroyers myself alot. This game is hard. However once the pings hit your boat it is almost certain that they know where you are. Forget all the stealth and dodge as fast as you can. Chance depth frequently, course slightly enough and most importantly pick up speed as fast as you can. Once you have made some ground, go for silent running of even full stop and try to turn towards or even better away from the destroyer so that your silhouette is as small as possible. Good luck!
(fyi this is coming from a guy that in his last game got hunted for 2,5 hours and still got sunk in the end
)
4. From what i know, they can hear you if you turn the valves too excessively and blowing ballast will be heard too. But don't quote me on that. Just touch her very gently, your boat may not be a virgin after a good couple of patrols anymore but she still likes to be treated as one
