[the dark knight]

I am not sure about the type VII or the type II, but I do know that Type IX captains would cruise around 7-8 knots to and from the patrol area to conserve fuel during the war. I do this in my type IX's in game, and once in my grid square, I will search in a ladder pattern. There are also defined shipping lanes that I like to cruise in on my way to and from a grid square. (these are shown in the GWX folder. I found them through trial and error in stock SHIII)

You will need to rotate your crew manually, unless there is a mod out there that will allow it automatically.

I do most of my searching on the surface, and will search with the hydrophones at night or in bad weather. That is early war, later on you will only be safe at night on the surface, so you will need to stay submerged during the day instead.

I would say do not dive in anything shallower than 20M with anything other than a type II. If a merchant sneaks up on you, it will ram you and you have no where to escape to. As for how to know the depth, your navigator can tell you the depth under keel.