As for questions 3 & 4.
I've joined AI subs to a British convoy, I placed them a few miles away, they eventually join the convoy but when they get in range they open fire and the battle commences.
Try making a small convoy and then join the subs, have them on a kind of collision course, place yourself a bit behind them and watch the action on external camera.
I've done the same thing with AI ships too, great fun.
