I doubt level will have much to do with it, they likley only asked for levels because they want to make sure you have at least 1 character over 10 which is what you need to be for Dawnguard. I'm still hoping forum activity and when you applied count the most.
Well also, if people are beta-testing then they probably want to check different levels of character ability for balance purposes.
I applied, hope it all works out. My luck has been riding high.
I like the questions they asked. Trying to cover a wide area and a wide range of variables, it seems to me. I don't know how many they intend to give, but it's probably a fair amount. It's a pretty big amount of content from what I can tell, they'd need a lot of people to test it effectively.