If you want good (legal) software then you can't go wrong with the GIMP (
http://www.gimp.org/). It does most things PS can do and its free - can't argue with that. To convert to B/W it's best not to just press "B/W" options. There is a thread on here somewhere linking to an excellent website that gives you about 10 different ways to convert to B/W. Your starting image is already quite dark, so doing it carefully could give good results. You will find that most B/W photographers shoot with a strong colour filter top side, this can significantly change the appearance of the final image - in software you're just doing the same in post processing.
Autofocus is always a pain to get used to and one of the biggest let downs you will ever get is when you think you've got "the shot" and once downloaded its out of focus. Try taking photos of flowers topside, best of all in a darkened room to get used to how the focus performs in low light. Low light = low f number = very restricted depth of view. It's always tempting to get the camera that little bit too close....
As for the Red Sea, we are shore based. I just hope I don't end up with a "follow my leader at 100 miles an hour"-type guide!
Rob