Go ahead, put your hand in the tank to get the damsel. The lion probably won't harm you, but wash your hands first to make sure it doesn't smell like food. If you hand feed, watch out, 'cause it will associate your hand with food and could try to get food from it.
Feeding: try to get it to feed on frozen food, the sooner you get it to do this the better. DO NOT feed FW goldfish. To get it to eat frozen, spear the forzen food on a feeding stick, and wiggle it around to make it appear live.
You may want to reconsider keeping it in a 90 gallon. It should be fine, but keep in mind they get huge. A good analogy that OrionGirl said was "its like a basketball floating in your tank.
Good Luck with your new lion. They truly are spectacular fish.