My tip is to post your listing on a Friday evening / early Saturday morning. Since most 9-5 programmers aren't bothered to respond during their free time (aka the weekends), your chances of finding a passionate / committed programmer will be much higher then. Also, make sure you put in ample details about your job on the listing.
Just my observation.
Also, if you want good hackers, you must be willing to pay good money as well (and be sure to talk about that in your listing as well).
Edit: forgot to answer your question: yes, a decent outline should suffice most of the time.
This is important, since professionalism is a huge factor in how well freelancers perform. You almost certainly want to work with freelancers that work predictable daytime hours and can thus respond quickly when you have questions.
I certainly don't mean to suggest that someone working on a weekend can't be professional (I'm on HN myself right now). But I don't think it's wise to intentionally avoid the 9-5 crowd.
Instead of posting a description that anyone can respond to, we'd setup a brief phone call where you and I can discuss your project. I'm a developer myself, so I help you figure exactly what sort of experience would be best for your project.