start off with only 1 frogfish for now...they can eat each other. They can eat anything upto and including a little bigger then themself. So 2 frogfish will more than likely quickly become 1 fat one.
They also produce a lot of waste, so 1 in a 12 gallon is probably enough. Frequent water changes is important, and you will start to see their poo on the sand and will have to sift it out.
Liverock, you do not want a lot in there. I only had 2 pieces (small) in mine. They are very, very stationary animals, and if you have too much rock in there you will never, ever see them as they will pick out one spot and stay there most of the time.
The size depends on which type you get. A 12 gallon should do fine for a long time. There are some frogfish that get very big, but depending on the size you get it, you should be able to keep it in there for at least a year or two.
You do want to make sure that your fish is eating very well before you buy it. They can be difficult to get to eat. Mine ate ghost shrimp and I set up a breeder tank of mollies, which he never was interested in, so I had to keep buying the shrimp. I tried to switch over to frozen but was unable.
Make sure you do a lot of research on frogfish before you buy. There is very limited info out there on the net surprisingly on these fish. They can change color depending on the food and the enviroment you have. (red sponges in tank might turn fish red, as they mimic the surrounding) You want to make sure you gut feed the live food with vitamins and fatty acids and feed whatever you feed them good quality food. I always supplemented my shrimp with either Selcon or Amino Omega vitamins with their meals and then I would soak the shrimp briefly in the Amino Omega (By Brightwell) prior to feeding. I fed my feeder tank the same food I fed my other saltwater tank. What goes into your feeder goes into your frog.
Do not ever net a frogfish when you transfer it...just like a puffer. Can get air trapped in stomach and die (Did not know that when I got mine). Not sure what happened to mine, but just lost my frogfish a couple days ago (bad week to be a fish in my household
). Was doing really well, and all of the sudden started swelling up to the point his eyes were barely visible and died. I did not move him or anything, so not sure what happened. LFS said possible bad shrimp? Ironic died of food poisoning!
Also, no goldfish..they are unable to digest the oil or something plus the skulls can get blocked in their gut and can kill them.
Most of the info I found on them was in some book my mom bought recently, and I can not remember what it was called. I will try to get the name of some of the sites I used and the name of the book and post it back for you. But in the book my mom had, the author was showing how he had a black and orange spotted fish that in a matter of a month turned to orange with black spots due to the feed. My fish turned from yellow with brown strips to cream white. My moms was red and turned yellow with red spots and now is turning red again.
There is an article in this months Coral magazine that had a little article on Frogfish that might be helpful...not a lot of info but some info about how they lured prey in and also used mimickary.
They are definately some cool fish.
Good luck and I am going to be on the look out myself for a new one. This time I think I want a bright white one with orange spots (at least that color for a couple days :}
Frog fish? 
