I think your experience should be a big plus. Even though it isn't exclusively in billing it will be helpful. As far as whether or not it will be easy or tough, there is no way to tell. However, you need to exhibit confidence when you meet with your prospective clients in order for them to be confident with you. Some people have tons of billing experience, but no confidence and won't land the account, while someone else may have no experience but is very confident and signs the provider on the spot.
Good luck!
Michele