This is not an easy question as there are many items to consider. Management structure, wages, job descriptions, benefits offered and more. Turn over is a costly part of business, instead of asking the question what is acceptable, I would ask what is not acceptable. Make changes, get insight, conduct exit interviews and find out why you seem to have turn over. Make adjustments accordingly.

You would not “tie up” your SSN. The purpose is so that the Government can track your income. You must if you are the managing member of the LLC or officer attach your SSN when applying for an EIN. I would also caution you that you provide accurate information.