I certainly appreciate your ideas to be creative. As a newbie myself, it’s something i often hear about but am not totally sure on all of the parameters. My two cents...
Once your partner buys the property via an FHA loan, anything you do to try and add your name to the mortgage or have an LLC take over the mortgage, triggers the due on sale clause.
I also don’t hear about people working out creative partnership deals for house hacks. Typically, house hacks are done by a single person or spouses. I think trying to make that work could potentially cause problems and may not be workable.
If i read correctly, your partner wants to bring you in primarily for your property management skills? If that’s the case, why not be his property manager and skip the ownership stuff?
Another tidbit, I’ve never heard of a partnership where each partner is assigned certain units to operate. Typically, the duties are divided up and the profits are shared. If you’re both operating each of your two units, it sounds like there’s going to be a lot of duplication of efforts and possible issues.
If your both truly want to be owners, you could try and find a portfolio lender or use a commercial loan for the 4 unit. Both permit LLC's to be owners. Obviously, the terms are different and may not be as appealing.
Why not pool your money and get a larger deal?
Good luck.