Finfighter,
I think a lionfish would be okay as long as you give it plenty of swimming space, live rock, and feeder guppies. I think it's a pretty calm fish and not aggressive towards it tankmates. I have s dwarf lionfish, two percula clowns, one blue damsel, one yellow tail damsel, a coral beauty, a cleaner shrimp, and plenty of snails and hermit crabs, The lionfish does not bother any of his smaller buddies which he could easily eat. He hangs out by himself. I would add him towards the end. I think the aggressiveness of lionfish is over played.
My lionfish has gone two-three days without eating and he doesn't bother any of his tankmates. But once he sees the guppies he goes for them. Just one thing you should be careful when getting a lionfish: make sure he is healthy and free of disease.
Good luck on your future fish-eater!:happyfish