Questions:
1. What is an "agency-direct bill patient"? You need to ask the agency this.
2.Will getting this NPI for the national company, in any way create a problem or influence me getting my own NPI for the physical therapy company I wish to soon start on my own. I am only doing the on-call work to supplement my income while I grow my own company. You will be obtaining an individual NPI, that will stay with you whether you work for this agency or for yourself. It will not create a problem. You will be getting your own NPI now, but they will be using it to indicate that you rendered the services for their agency.
3. In starting my business---at what stage do I need to get my NPI number? Will I need a second NPI for the company itself? Should I get both only after I have a business license? You need to get your individual NPI now. If you establish a company, you will need a type II NPI for that company once you establish it. You should get your individual now, and your group once you have a legal business name & EIN number.
4. I plan to initially have independent contractors work for my company. What requirements will there be for each of them to have an NPI number or will they bill under the companies number? They will need their own individual NPI numbers and you will have to credential them under your group.
5. Getting started, can I bill and work as a sole proprietor under just my own NPI---then as business grows switch to an LLC or S-Corp and then get an NPI for that new entity? yes.