The best way to test an idea is to begin to execute it, which is why a lot of founders say that success is something like 10% good idea and 90% execution. Think of your "overwhelming excitement" as an asset and dive in. But, be systematic and organized. Design your task list as a series of tests. Start to build, but critique at each step. If the idea cracks and falls over, then it was weak and it's time to move on.