I've had great luck with a hex tank and freshwater, granted mine is 22g... I have yet to take that success into salt, but one thing I would say is that lighting will be the biggest issue since they are un-proportionally tall, I would seriously look into some DIY LEDs, or maybe a LED PAR bulb to light this tank all the way to the bottom..
Look into mushroom coral, very easy to keep for the most part... In fact most soft photosynthetic corals are pretty easy to keep.... Zoas could be an option as well...
The thing that you WILL NEED TO DO, like religiously... is water changes... With no nutrient export, you will need to do large water changes VERY regularly... I would start with 1-1.5 gallons a week, if you start seeing problems start changing more...
As for fish, keep it easy... and try to get fish that are going to be beneficial to your tank... Look at these possible fish:
*Two spot Goby - sand sifting goby, fun to watch, keeps your sand clean
*Neon Goby - cleaner goby, pretty fish
*You could have a watchman goby/pistol shrimp pair - fun to watch, keeps your sand bed moving...
*Firefish - beautiful fish for the price, note, they are jumpers, you'd need your tank covered... also, they are kind of skidish and need places to hide
*Yellow Headed Jawfish - fun fish with great personalities, note, they need a deeper sandbed to be happy
*Barnacle Blenny - awesome little fish, great personalities, note, they need lots of little places to hide
*Yellow Stripe Clingfish - interesting looking fish, preys on parasitic bivalves that could get into your tank, note, they like to live in either a branching sps coral or a longspine urchin
As for a clean up crew, go with snails, you don't want to deal with hermits that get too big for your tank...
Hope this helps, and good luck!
