Not sure of the terms etc, but I did tell him that he can work on repairing his credit and refinancing out of the owner finance loan down the road, so even if 30 years of payments he isn't bound to that one loan and rate.  

I enjoy fixing and repairing items, it saves money resources and it also allows me to look in on my units.

A good thing about the Primary residence is that if you had done repairs while doing some improvements to the house, you can add the repairs to the basis of the property too.

Two of the units are currently rented for $750 each, while the third unit is vacant and currently undergoing repairs.

If any of the utilities require an inspection or any repairs do to their inspection you are out of luck as HUD allows no repairs prior to closing .  

Though he was telling me it's impossible for him to give 100% accurate repair estimates without looking behind the walls.

My plan is to finance with an owner occupied conventional loan, live in it for one year while making repairs to the one bedroom side, then move out and rent both sides.

No matter what class the property is you should be providing a clean, safe home in good repair.

But I would make sure you take into account all expenses (taxes, insurance, property management, repairs, CapEx, etc.) to determine monthly cash flow.  

I am looking at deals that all in after repairs will likely be  under 100k.