Your real problem isn't how to hire, your core problem is "what is the best way to communicate the scope and details of the project?" If you're asking this question it sounds like you don't have a specification or a prototype: If that's the case it's a good idea do to that step first before hiring a developer.
I would finish the wireframes, make them as detailed as you can -- and then talk to a few developers. It might be a good idea to work with someone with UI/UX experience if you feel like your own wireframes are too fuzzy.
