First deal! Low income 4plx owner financing!

[Nolan M.]

After a few months of looking I've got my first deal in the works. Unfortunately its 1 1/2 hours away, but its 100k less than similar properties here in the Mesa/Phx area. I figure I can manage it in the beginning and then hopefully find a competent property manager that doesn't charge too much if i need to. Its a 4plex built in 1980, all 2/1, currently 100% rented at $500 each. I'm borrowing 30k from a family member for a down payment and the owner is financing 120k at 4%, 30 year term. Landlord only pays for trash, which is about $50/month, all other utilities are individually metered. One issue that the owner has brought up is that sometimes he has trouble filling the 4th unit, but said that is primarily because his daughter, who manages it for him, isn't always diligent about advertising it. 

So the primary mortgage will be $575, I'll be paying $250 to my family member, and trash, tax/ins will be about $200 for a total of $1025. I think worst case scenario I'll be out 30% for vacancy, CapX, and management which still leaves $375 cash flow. 

Any advise and insight would be great, thanks!