Yes, I can offer some advice which is based on my opinions. I am not an accountant, and the following is based on my personal viewpoint on these issues.
You have a small business which will never be a big business. Incorporating will not benefit your business but will benefit your accountant because he will charge you more for his services.
It is not necessary to have a separate account for your business if you keep accurate records of all business income. If you want a separate account, set up another free personal account under your own name and use it for a business account.
You can get an EIN number and use it if you prefer but it is not necessary. Some people prefer to use the EIN because they feel it is safer than putting your SS number out there in a lot of different places. I have an EIN for those few companies who prefer it, but I have used by SS number in the mystery shopping business for several years without a problem. Some posters on the forum have provided information indicating that getting an EIN number in some areas may generate additional taxes and reports on state, county, and local level. You might want to investigate this thoroughly before jumping in with an EIN number.
My most important recommendation is discuss your situation with some more accountants. Your accountant is trying to set you up as a corporation because that benefits him, not you. I would suggest an accountant who specializes in very small businesses set up as proprietorships, which is what you are until you incorporate. Incorporation for a mystery shopper will be unnecessary and costly.
To protect yourself on the liability side, be sure your automotive liability insurance covers your mystery shopping driving.
Mary Davis Nowell. Based close to Fort Worth. Shopping Interstate 20 east and west, Interstate 35 north and south.