IMO, fins are just a matter of preference. As someone alluded to above, a large solid fin can give you a leg cramp if you push too hard. A split fin doesn't generate as much resistance, so that's less of a concern. In practice, just about any fin will work fine, just get one that's comfortable on your foot and doesn't pinch or bind.
A dry snorkel has a device on top that prevents water from entering the snorkel tube. A semi-dry has a flap or cover to keep water out, but isn't as robust. Up to you if you think these are worthwhile. Some people like them if they're going to be snorkeling in rough water, it reduces the chance that water splashes into your snorkel. Personally, I'm perfectly happy with a plain open snorkel. When it fills with water when I dive below the surface, that's just less bouyancy that I have to take down with me. With a little experience, it's very easy to clear the snorkel when you surface by forcefully exhaling through it. I think some people like the idea of a 'dry' snorkel when they're just starting out, since it alleviates a fear of sucking down a mouthfull of water.