At first, it seems odd that Tetsuzan Shogun just happens to have a Miss America costume ready for use when he didn't know about Diane in the first place. Then in episode 24 we learn that Maria trained under Bosner in America, just like the four guys trained in different countries. When you take into account that the Battle Fever Robo wasn't ready until the fifth episode, you get a clearer picture of what actually happened: Maria was always the one supposed to become Miss America, but when Egos attacked sooner than expected, Diane had to fill in for her (presumably Bosner knew of this, and that's why he brought Diane to Japan with him).
Why is Battle France incorporating Spanish dance moves in his fighting style? Well, France—especially Southern France—has a lot of Spanish immigrants due to the Spanish Civil War.