The bigger the tank the better--but I would not mix a volitan with dwarves. Volitans will try to eat anything that will fit in their huge mouth--and an adult volitan could eat a dwarf lion, though it wouldn't be a good meal. In large tanks, volitans are actually very active swimmers. I've seen a trio in a 240, and they were always moving around. A gentleman in NY has one in a 400, and that fish is seldom sitting around, either. Adults will be about the size of a basketball, and won't swim around if they don't have enough open water to avoid catching their fins on rocks and such.
Avoiding a sting is mostly a matter of paying attention. The lion will let you know when you're annoying it--they tip nose down and flare those fins. My lion would get ticked off during glass cleaning, but he was easy to avoid--I'd just work on another section until he cooled down, then gently shoo him away to another spot. Moving him was the scariest--couldn't net him (didn't want to damage his fins), so had to scoop him up in a large bowl, and then avoid the thrashing fins.
If you are stung, run the area under the hottest water you can stand--the high temp breaks down the toxin quickly. Hurts like the dickens, and can cause an allergic reaction in some people, so caution is a good idea.
