I'm currently working some freelancers on my HypedSound relaunch. The designer and frontend coder both worked on hourly billing but everything was very well-defined. Since the backend is a much more complex scope, it was hard to define hours, and I'm working with a 'variable scope and budget' that we're shooting for. I wasn't ready to commit to hourly billing. Luckily, I have an advisor looking over all the code, which I think is essential as you mentioned. Whether it's a language barrier, technical barrier, or incentive barrier to good communication, you should have someone technical on your side even if they're not doing the coding.