I would advise moving the lion out before you get other fish. They're cute, but they don't play well with others, and the more moving bodies and excitement, the more "on" a predator gets.
A good mix of easy-care fish for a 90 is: 3 bluegreen chromis, 3 pajama cardinals, a lawnmower blenny, a watchman goby, and a royal gramma. That combo won't eat each other, they'll be up and moving (cardinals are the sort of fish you sort of move to dust under) and they don't get most diseases under reasonable care. Get yourself a fighting conch, and some basic mushrooms and buttons (thrive in medium-care water and under dimmer light) and you'll have a colorful and impressive tank.