Welcome Aboard!
Short answers below. As mentioned, look through the stickies. Also, find a post by THEBERBSTER, such as
this one, for some links to get you going.
1) Yes, it is.
2) Passive is peeking out the window to see if you see anyone. Active is turning on a spotlight and shouting "Is anyone out there?" Active is much more likely to get you noticed than passive.
3) It's a depth at which water temperature changes drastically. These layers do funny things to sound, which means that the enemy is less likely to hear you if you are below the layer.
4) Go too deep, and your boat will be crushed.
5) Certain technologies are time-dependent. The empty slot still appears, even if the device is not available. It also depends on your home port. Pearl Harbor gets new technology faster than the Australian ports.
6) The skills are important, and the fatigue level. If you forget and leave the crew at battlestations, they'll tire out after a while and refuse to do anything.
7) Depends on what mods you are running, I believe.
8) I think so, but I don't remember which file controls it.