I am no expert but i recently did a little reading..
The frogfish will do best in a tank from 5 to 20 gal. size tank. They are best kept alone,with no other fish. They can eat fish up to the size of their body and can cause trouble in your main tank if you have fish and inverts.
They also change color, so don't buy an angler for the color. You'll get a nice red one for 50 dollars and theres a brown one or 20, chances are(dependingon the color of surroundings in the tank) they'll change color. Which takes a process up to a couple weeks, to months.
If you are to keep an angler in a tank with fish etc. Then you must buy something to add one color to the tank for the angler to hide in and adapt. Like i said, they do best alone in a tank. YOu can even go with a 10 gal or even a 5 gal. Which will be harder to maintain, but much better for the frog. getting 2 frogfish would not be the best choice since these creatures can be cannabilistic. If you would likea mated pair, look for an angler that is much larger than another, just one way of telling. This tequnique isn't the best, it's hard to identify a male from a female angler.
I did some reading at the bookstore from a latest magazine and just basically am telling you the facts. THis is not from my head.
HTH