Help structuring a condo conversion deal

[Kati Stratos]

Hello! I found a great off-market opportunity with an eager seller and would love help thinking through the best way to structure this deal.

 Property: A beach-block 4 unit multifamily at the Jersey Shore valued around $850. The seller wants to keep his unit but is sick of being a landlord for the other 3 units. 

Deal: The idea we've mutually come to is that I would purchase the property from him for $650k and convert it to condos, and then sell his unit back to him for $1. I've spoken with a lawyer and am not intimidated by the condo conversion process, which seems intense but fairly strait-forward. 

Question(s): How should I structure this deal? What happens (legally) with the sellers unit if condo conversion doesn't go through (for whatever reason). From what I've read, one option is to purchase the property as Tenancy in Common (TIC) with 25% ownership to the seller, 75% ownership to me. From what I'm reading, it's hard to get a lender for a TIC. Also, how would the refinance work after conversion? At least 2 units (sellers and mine) would most likely be owner occupied, though not as primary residence (as vacation home) - would that complicate anything down the line? The remaining 2 units I would plan to either sell or keep as vacation rentals (its a huge vacation market and I own/manage other AirBnBs in the area) - am I allowed to keep more than 1 unit after condo conversion?

I'm looking for someone who has some experience with this and could help me think through options, landmines, creative ideas, etc. I'm not sure if I should start the conversation with a lender, a lawyer, a developer, my broker (I'm a licensed agent), etc. so I'm starting here! 

Thanks so much in advance.

-Kati