I have a client selling her business. She will max out her SIMPLE IRA before she sells, and will then work for her husband in a different business. We’re thinking about doing a Solo 401(k) for his business. He has no employees, and no company retirement plan. Can he do this, or are they considered one entity for retirement plan purposes? Does he technically need to open a SIMPLE IRA? If she can contribute to both plans, how much can she contribute in addition to the maximum SIMPLE IRA contribution? She is under age 50. Thank you