Well with a small tank it all depends on the size. bigger the tank the more choices you have. Anemones are usually out of the question for small tanks since they get rather large in comparison to the small tanks. I'm slowly making mine a reef but they are much more expensive and time consuming than a regular tank.
Maintenance weekly water change, possible mid-week top-off to maintain a steady s.g. Reef tank depending on your corals.
Depends on the tank size, smaller like mine goby, larger like 10 or more gobies, maybe clown etc.
Depends on whether reef, everything that you would need for fw plus powerhead/s stronger lighting, if corals more test kits, stuff like that.
A smaller tank isn't really harder to maintain, it just takes more dedication but it's really not that hard at all. I would suggest go for it if you can keep up with weekly water changes and do the research because it's really not that hard and it opens a whole new world.
