Good job on separating the lionfish and deciding to take him back. I am sure your other fish are very grateful.
A single dwarf lionfish takes up a very large bioload. They need meaty foods and are messy eaters. There is also a very high chance it will see your other fish as food. Usually lions will try to eat anything they can fit in their mouth. I wouldn't add one with your current bioload and livestock.
If you want a different nano fish to add then I would research blennies and gobies. There are many colorful species with great personalities.
A single dwarf lionfish takes up a very large bioload. They need meaty foods and are messy eaters. There is also a very high chance it will see your other fish as food. Usually lions will try to eat anything they can fit in their mouth. I wouldn't add one with your current bioload and livestock.
If you want a different nano fish to add then I would research blennies and gobies. There are many colorful species with great personalities.