Size won't matter, as they will grow. I would get the biggest Puffer you can find (In the toby class) and the biggest Sixline you can find. The Lionfish will be ok. Anything that can't fit into it's mouth.
Lionfish like to perch so make sure you got a lot of live rock for him to sit on. Also you will have to whine him/her over to frozen food. That will take some work, but what you can do is get a pair of feeding tongs and some Silver Sides or Krill (Very his diet so he will not get board with his food
. So just like fishing, you will dangle it in front of him in hopes he will eat it. Live Ghost Shrimp is fine for a while, DO NOT FEED HIM LIVE GOLD FISH!! Freshwater food is bad for him, and it will not sit well in his stomach. So as soon as you get him over to frozen foods the better (thawed out of course). They are really not that mean of fish, but again I just didn't have time to feed a lionfish like I needed too. So I went a different route, plus I wanted more colorful fish!! :-p The Lion fish is a real cool fish, and if you can keep him healthy, you should have a great fish. The Sixline is also a good looking fish, and helps in keeping pest down in your tank.