You mentioned AOB, on thing I would suggest is downloading the mod easy AOB it makes it a elot easier when starting out with manual targetting, at least did for me.
Also I personally wouldnt suggest turning the map contacts off - at least give yourself some tracking chances at the start.
If your using TMO which I think you are the attack map has the bearing plotter that allows you to see the impact point of your torpedo something which when starting out is useful! Think it's the Rocking Robbin tutorials that show this at work, as previously said by WitoldGritz check out the videos they help a lot.
And finally good luck and happy sinkings
