The first step would be to write down your idea, in as many details as you can come up with. In other words: Write the design document. Usually, while writing down in detail you already spot where it works and where it doesn’t. I’ve personally scratched a couple game concepts at this point because when you think about it in detail you figure out that it actually doesn’t work the way you thought it would.
As for protection: Forget it. Your idea isn’t worth protecting. The design document is. Protect it by sharing it with others only under NDA. To recruit a team, you want a short version of it (one page, two at most) which doesn’t deserve an NDA.