The puffer will be about 4” and should be fine. The lion fish will be slightly larger. The clowns will be about 3” each. They will all fit but consider this.... you won’t want but about 1” of full grown fish for every 3-5 gallons of water. So in a 45, you can have about 9” of fish. You could do two 3” clowns and the puffer maybe. Or you could have the lion.... but.... lions can become very sly and may eat your smaller fish if given the chance. Putting the eel in her own tank is very wise. The lion could go with her. They are both predators and would get along well together. I would get the eel in her own tank quickly, depending on how big she is. She’ll grow fast. The other day, a moray belonging to a friend, ate his 6” powder blue tang!