Self Directed Solo 401K and DQ for S-Corp Share Ownership?

[Cameron Price]

Hello 401K gurus and Tax Specialists! I have a couple questions I haven't found eslewhere.

I'm considering a partnership of some sort with another landscape contractor. We are unsure how to structure the arrangement. I'm consulting with my CPA next week, and had a meeting with a financial advisor today.

My current situation (sole proprietor with no w2 employees) qualifies for me to start a self directed solo 401k. This retirement setup is important to me, because I want to use the roth feature, max out the 18K roth contribution, and use that to buy rental property inside the 401k that can be improved, rented, and/ or traded up inside the account all tax free.

My concern is with forming a separate business that will have w2 employees. Which of these would disqualify me from having the solo 401k account with my current business. .

50/50 partnership

49/51 partnership with me being the 49

S-Corp created by the other guy with me having 50% of the shares

S-Corp created by the other guy with me having 49% of the shares

If you have another structuring suggesting that would allow me to keep the solo 401k, feel free to add it. We already work together as separate companies, but want to go bigger and need to structure things properly. Any advice is greatly appreciated.