To answer the question regarding a "well-fed" lionfish, they should be fed about 4-6 appropriately-sized (about the size of their eye) food items 3x a week. We feed M-W-F with weekends off. If you feed more, do it every-other day at most.
FWIW, one of the arguments for feeding lionfish (and other preds) non-living foods is variety. Feeding any single food in excess generally means your fish is missing something in its diet.
Target feeding is great, because you know exactly how much food each fish is getting, whether it's eating at all, etc. At this point, you're interacting with each fish, and it's easy to see how it's doing, and another important thing is that your fish gets to know you, which is great when you have to work in the tank (they will be a lot less skittish).
It's also fun to stick feed your fish rather than just popping the food into the tank.
Altho having a stick-trained fish won't necessarily make them less prone to eating a tankmate if it's feeling peckish, I can say that most of our fish are so well-trained, they will ignore live food in favor of the food on the stick if both are offered concurrently.
I use some long tweezers. Some use plastic feeding sticks and some with finicky lions use fishing line.
It's not necessarily that the fish are finicky, but many are intimidated by some huge "thing" waving around in their tank, and still others have accidentally bitten the tweezers, stick, etc. and didn't like it.
In answer to this, we came up with what we call the "stealth stick", which works well for pretty much any fish of any size (we actually hold a patent on it). They're easily made with acrylic rod and 50# test monofilament: