Any tips on what I should be asking for?
As far as skills go, just look for programming skills, ideally with a body of completed prior projects. Hopefully the projects are somewhat large and/or complex (not a GitHub profile with a few forked repos and toy projects). Of course, many good developers have no publicly available projects but as a non-technical person you will have a hard time judging those people and they're probably not the type to work with you anyhow (they want benefits and paid vacation).
I'd recommend something like Craigslist - Computer Gigs or if you want to pay someone market rates, Craigslist - Internet Engineers or Stack Overflow Careers.
Also, if you are paying market rates, you should reframe how you're explaining this. The gal/guy with an idea in search of a coder on Elance is a pretty poor first impression. Just say you're a bootstrapped/self-funded startup. And make sure to do your share of the business side of things which somehow most non-technical people aren't actually good at. Line up paying customers rather than taking a Field of Dreams approach.
No offense, but if you're non-technical, what are you basing this on? Literally every client I have worked with has said this and it's almost never been the case.
And as for your actual question: the most important attribute you should look for besides basic technical competency is someone who really believes in your idea and wants to see it through.
Looking for the lowest bidder on Elance will result in a lot of pain for you. They will see your baby as just another project to knock out. They won't have you or your business' best interest in mind and will cut corners. You will end up spending a lot of money for a low quality result, and other developers likely won't want to touch it.
Unless you have the money to pay a full time, market-rate salary, you will have to find someone who doesn't need a high salary (although they will expect a significant amount of equity, like 10-50%) and believes in your idea enough to deal with lots of iteration without cutting corners.
If you cannot do that, then why are you trying to build a tech(ish) startup when you are afraid of using tech to build it?
Here's your 3 options: Rails, Django, Meteor
All 3 claim to help make rapid prototypes, so use/learn one and push a prototype out in 2/3 months.
I promise I'll upvote you if you do.
The beautiful part of Magic is the simplicity of just interacting through text. If you generate enough interest you can worry about scaling it up later.