Here are the number:Purchase price: $320,000Amortization: 30 yearsInterest Rate: 5%Balloon payment: 3 yearsMonthly payment: $1717.00How do you structure/allocate your monthly payment to the seller (i.e. amortize 30 year repayment schedule, interest only, or a larger set amount as principle, etc.)?

Arbitrary rules are hard to program, principles are much easier for an automated system. 

The same basic principles apply to investing in real estate.

Of course, I paid the down payment, have already significantly paid down the principle, and obviously run all the operations for the rental. 

No one gets paid.Utilities could be either common areas and office and/or there may be a Rubbs or bill back to the tenants.Mortgage interest is the mortgage without the principle pay down.

In principle, borrowings for no return = BAD debt.

So, I call it, "The Einstein Principle".That is, notice whether what you're doing is producing the desired result.

NO way I buy sight unseen even if I have to break into them.

I have a few FSBO's in my sights, including one that rejected my initial cash offer a few weeks ago that I'm going to re-approach with an LO offer this weekend.

One principle I have always followed is that there is never harm in asking.