[cheetos]

> It seems like a straightforward backend

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.