I had actually thought about competing here in Virginia. There is a competition next year in the DC area. You don't have to be a professional to compete.
I'm sure they all have different rules, but for the one I am thinking about competing in, they allow cake dummies, which will be my cake of choice. I probably would start sometime in January decorating it so I didn't have to do it all the week of the competition. I don't care if everything is as hard as a rock! I will have to drive about 3 hours, so the harder, the better! :)
There is a cake tasting part, but that's separate and you don't have to participate in it if you don't want to.
From what I read, there are about 15 or 20 different categories you can compete in, and they go by your skill level. You choose what you are, but they give guidelines on how to figure it out.