Nikonos V w 35 mm, red filter, available light using Kodak 800 Max film. A hard-shell case protects your investment. It's worth it. Film choice can be complicated, or easy. So you want to use the slowest film that you can adequately expose.
Magazines can more easily judge the quality of a picture from a slide.
Also, good-quality slide film has a finer grain. Buy good quality. You should start with 100 ASA film. When you find an old roll that's been in the trunk for 5 years, don't use it for your next scuba photos. Save it for something less important, like your next wedding.