"One becomes dominate and the other may change to female to form a mated pair" the female is the dominate one.
Just buy two that are close to the same size, they'll fight it out later.
"do not swim too terribly much" No way would I put my clown in a 10gl, she swims all over.
"I'm all ready going to put one in" the tank is cycled right? (just making sure since you are new to this board, and many don't know they should cycle the tank before adding fish).
good luck