Hey 7gJoe
Welcome to salt. When you say a "nice amount of sand", how deep exactly? A hot topic with nanos is the issue of sandbed depth. Current thinking is that with this small of a footprint, it's near impossible to sustain the sandbed fauna needed to prevent oxygen debt in a DSB. I would personally use no more than an inch or so. You should get sufficient denitrification from about 10lbs of high quality liverock.
As for temp, anything from 78 to 82 should be fine. The key is keeping it stable, not hitting a specific number- not always easy in tiny tanks, especially when you take into account heat from lights. You may have to employ a fan to accomplish this. A fan would, of course, increase evaporation which is another major concern. Disasterous salinity shifts can occur very quickly in small tanks. Daily top-offs are a must.
Don't even consider an anemone. They're really not suitable for tanks this small. But if you're looking into one, I would assume you've got decent lighting above the tank? If so, go reef. You can create an amazing display of soft corals and LPS in that tank. One fish is as much as I would do, especially if you're going to do a reef. As for crabs, most non-hermits tend to become problematic in little tanks (in big ones too, actually). If you want something sci-fi looking, a skunk cleaner shrimp would be perfect. They've got tons of personality. Feel free to contact me if you need any help. I've been running a very successful 10g nano fully stocked for close to a year. You may also want to stop by
www.nano-reef.com There's a boat-load of folks there dedicated to small reef tanks. Best of luck and have a blast!