Getting the strategy for subsequent purchases set up before making the first purchase is VITAL.

If they're not flexible in price, you're wasting your time doing anything else except follow-up with the seller. 

I found a property manager that seems great on every level...except one.

Except in very rare cases, they don't stay A-class properties over time, @Kristopher Raepple.

They could have an exception for emergencies like the monoxide detectors are not installed or if they are and monoxide is leaking into the house from a cracked heat exchanger or non functional flue liner leading to an emergency safety situation and you were unavailable and didn't respond. 

But I also generally am investing in pure cash flow markets (The Midwest...except for some recent investments in Phoenix).If you stay around that 2-3% range, what's the worst that can happen?

If you play your cards right, you can find a lender who will allow you to use the "delayed financing" exception to do a refinance without having to wait the usual 6 month seasoning period.  

Once its programmed to capacity, you will find it a vital organ in your business model. 

Of course there are some exceptions to this, depending on the area.

It is just like any other loan except the lender is the seller.The two concepts are separate, but can be combined.An example of a sub2 without owner finance: An investor buys a house sub2, keeps the existing loan in place, and uses the house as a rental.An example of owner finance without sub2: An investor owns a home outright.