Alky- I'm not much further along then you on experience, and also came to SH4 from flight sims; comabt and FS2004. Some more knowing then I will certainly answer in greater detail. But until then..
>> I take it that I blaze across the high seas on the surface. <<
Yes..particularly at night.
>> What do I do if I see a contact on the map, dive, shut off engines & sit, wait till they get closer then dive..>>
I usually creep up a bit closer after teh map contact and go to periscope depth, and 1/3 ahead..or you can sit and wait if the target is coming toward you. The real experienced guys here can probably tell you half a dozen another tactics as well.
>> I've seen mention of surface attacks, is that just in real life or can you do it in SH4?<<
You can absolutely do surface attacks; depending on the target will probably depend on your success. I like shooting the "junks" and small merchant ships with the deck gun
The are many tutorials on just about every aspect of SH4..check the "sticky threads" and do a run through on the download section.
Royce