I hope I'm not chiming in out of turn, but this business has the potential to make decent money but takes a lot of effort to obtain and retain clients. You also need to understand that what the doctor bills and what he gets are very different. Each insurance has a different allowed amount for services, so the amount billed out against what is collected can vary each billing cycle. We have some months where we bill a ton of Medicare. They cut our fees by 50%, so there's a large amount billed and only 50% will be collected. Blue Shield is better, Blue Cross is worse, Worker's Comp. is on a set fee schedule and cascaded, Personal Injury is 100%.
It is VERY difficult to nail down exactly what your collections will be unless your doctors have a very specific patient base.
The gurus on this site have said over and over that flat fee works better than %, and in some states % is illegal.