If it were me, my first question would be to ask the billing company what exactly they were looking for....charge capture, straight diagnosis coding, auditing, surgical coding, claims submission, A/R analysis, provider education......then I would think about job descriptions and staffing to meet the needs based on the volume of providers and their expected turnaround time.
Do you have IT resources? research resources (coding books, online resources?). What software are they using and do you need to train people? What reports do they want from you? Be thinking about what their needs are from every angle...logistics, staffing, financial, policy/procedure, so that you can make sure you have exactly what you need right from the beginning.
Good luck!