Its not that difficult to keep, you just have to make sure it occasionally gets some meaty food. A few mysis/brine shrimp should do the job. If you keep feeding at the same time you can "train" it to open up at the same time of day. Mine used to open up every time I put my hands in the tank. It just seemed to know me after a while. That made it easy to feed.
You may notice it only opens at night. Thats normal but like I said above, you can train it to open at other times.
The only reason you may want to keep it from getting light is to prevent algae from growing on/next to it. As far as my experience, light has no other real effect. GreatfullReefer speaks the truth.
Your specimen looks pretty healthy. Starving sun corals (tubestra) look pretty bad, you'll know if its malnourished.
Enjoy it! Hopefully it will spread. Mine has.