How will you be setting the system up? Will you run a sump (highly recommended)? If not, what is you filtration scheme? A good skimmer will help too.
P. radiata will become too big for a 40B for sure. I wouldn't keep one in anything less than a std. 55 long-term.
For that tank, You could keep a couple of
Dendrochirus lions, maybe a fuzzy or barberi and a fu manchu and a couple of waspfish, maybe a cockatoo and a red-fin, possibly a small scorp if you can find something that will stay small such as
Scorpaenodes littoralis, S. carribaeus, or S. strongia.
As for stocking order, I'd add the waspfish before you add any lions, as the waspfish need to be established and weaned first for best results.
If you haven't already done so, get youself a copy of Frank Marini's excellent book
Lionfish and Other Scorpionfish (<$10 on Amazon.com). It's full of great info and photos.
You should also read his
Lionfish Care Article .
I also recommend:
Scorpionfish Care Guide
Tools of the Trade: Equipment & Techniques to Convert your Fish onto Frozen