So you want a school of clownfish correct? By the way fish can't count, thats someone just trying to justify that it works in the first place.
The groups you see in the store are there only temporaly and don't establish teritories usually because of that limited time in the tank and the lack of rockscape or anenome.
Clowns will generally pair up only to mate, ie....not social fish......and are territorial by nature....one clown or a mated pair to an anenome or frogspawn etc......
If you get a bunch of them you are going to a) cause them to stress out, and get sick and b) most likely establish a pecking order and kill each other off one by one until a single pair or just one is left.
However, it may be possible to get a couple of pairs in the same tank if the tank is LARGE, say 300 minimum and they are on opposite ends out of each others way.....
Think of it this way, clowns are one of the most popular fish, especially after that Nemo movie,(by the way the nemo fish is called a FALSE PERCULA), I would assume that because of that movie people would have tanks abound with schools of Nemos only. How many have you seen? Other than in holding tanks I havn't seen a single schooling group of Clownfish yet. Why do you think?
Decide on the specie you like, (I personaly love the maroonl/white or the orange skunks), and find them already mated if you want a pair. And find a BIG anenome to let them share.
There is a chart on the Marine Depot site and located on RC somewhere that lists the natural symbiotic relationship between anenome and clown species......I believe the false percula mates with the BTA, and a few others.....most will mate with any anenome except the Condy......My personal favorite is the Sebae, doesn't wander, opens up all the time with thick tentacles......
Some say Chromis in a smaller tank exibit the same trait and kill each other off one by one.
Below is a pic of mine, for scale the clown is about 4 inches long and the Sebae is 18"+