Typically, if you're making accelerated payments most people are trying to apply against principle, so no additional mortgage interest paid. 

Some of the most valuable books I’ve read (for RE) were not specific to RE but their principles were applicable.

It is the basic principle of an "income approach" valuation.

My reasoning behind this (although I'm not sure if I'm correct or not) was for a couple reasons: 1) It would (theoretically) keep my property taxes down. 2) It would (also theoretically) safeguard me against a market downturn, as I would have a lower principle balance at the time of refinance.

I never bothered to ask how he was getting compensated until we had negotiated the deal and agreed in principle with the seller on a price.

A banker is going to be looking a PITI (Principle , interest, taxes, insurance (+HOA)) vs income. 

Such as someone loans you all or most of the cash for the purchase and rehab and you pay them back both their principle and interest(simple) in however long you have agreed upon upfront.

Its just an option you can choose however construction loans are interest only.Some people choose interest only option for 1/3/5/7 years to enhance cashflow as you pay interest only and not principle.

It was an impressive sight!

I learned to refine this skill, while buying properties from the public auctions here in Florida, and by selling and buying many properties sight unseen.