I can only answer #1 and #3. Elephant ears are in fact a species of mushroom, but all mushrooms are distant cousins of anemones. So you could say that they it is an anemone, but to acurate, call it a "shroom".
The nutrition a goby can acquire from a sandbed can support it quite well in my opinion. I hardly ever feed my tank and my gobyis nice and fat, and I don't even have a sandbed. It feeds on detritus from the bottom of the tank.
Hope this answers some of you questions.
Danny