Linda;
Please note: my primary practice is tax research, representation and litigation. Notary signing agency is a ‘sideline’ in my firm’s practice.
Each taxpayer, individually, is entitled to only one SS number, and one additional EIN. Reference Treasury Regs. (26 CFR) §301.6109-1(f)(4)(ii).
If one has multiple sole proprietor businesses, such as someone who is an accountant, notary signing agent and teaches basket weaving on the weekend (no, I don’t teach the basket arts 
), they could have three separate Schedule ‘C’ in their return, each using their SS# or their sole EIN (their choice). I’ve dealt with clients having over a dozen Schedules ‘C’.
Normally, a second EIN would be rejected. If not, eventually, additional EIN’s for an individual will cause problems.
At the very least, the IRS will eventually revoke the EIN (their choice which one). At worst, you’ll be spending hours on the phone trying to get SS earnings credit applied and/or dealing with penalties for S/E tax that’s mis-posted and showing as unpaid.
As far as entity choice is concerned, we had a good discussion on this NotaryCafe thread:
I hope you find this helpful.
HWB.