I'm afraid I can't comment much on either issue, as I'm not that familiar with the rule book but I just looked it up a little. I know there are only four levels here, that don't quite match USASF levels. There's a specific level for youth aged kids. Then, for juniors and seniors there are basic (in tumbling, they can do walkovers, cartwheels and round offs), intermediate (all tumbling skills excepts somersaults). And then, there is elite for seniors only (everything is allowed up to a full if I read the rulebook correctly). I don't have time to study the stunts allowed at each level right now though.
About the mat size, I think that the mats in competitions are supposed to be 14m x 14m, but the execution zone must only be 12m x 12m (the same size as a gymnastics floor). In this video of last year's national championships, they had seven mats but the lines on the side made half of each side mat out of bounds. For showcase they had no obligation to use a seventh mat though.