Dave,
Your signature indicates you have a dsb but no live rock. If that's true, don't add fish yet, especially tangs. All sw fish are used to having lots of nooks and crannys to hid in. If they don't have them, they will stress and when they stress it enables parasites like ick to present themselves. Hippo Tangs, in particular, are hiders. They are very bashful and need places to go when they are scared.
If, in fact, you don't have any rock, you'll need to add lots before you add fish. Adding lots of lr will probably cause your tank to cycle again. Of course, it's a very bad idea to have fish in a tank that's cycling.
Lionfish are great to look at but they are aggressive eaters. They will eat most anything they can fit in their mouths and are particularly fond of invertebrates like snails and crabs. You should decide what else you want in your tank before you decide to add a lionfish.
Jim