My partner and I are beginning the search for some suitable doubles, and I'm running the numbers on some substantial commercial properties for the future, mostly as a mathematical exercise.

Well that defies Mathematics... 

I'm intimately familiar with the things you're describing  as I'm an Asset Manager who oversees right around 3000 multi family apartment units for a living.Again, mathematically,  looking for 50% DTI when you have rentals is difficult. 

Sure it is a step that COULD lead to a sale, but there is absolutely no mathematical correlation between the 2!

From a strictly mathematical perspective, having the debt, especially in these inflationary times, is probably the best plan.

Some folks place a really high emotional value on being debt-free.But no advantages mathematically to accelerate this loan (if it's long-term and fixed), especially since the mortgage interest on a rental is tax deductible. 

It is mathematics.

You can easilly have $20k in overages in a bad deal and take that $60k to $80k and then mathematically, you should've got the turnkey. 

The goal is ambitious: To ultimately convince 5,000 engineers to move to Miami.It's always best, as investors, to get in earlyDespite seeing an unprecedented surge in tech workers, the Miami metro area still only had about 60,000 workers in computer and mathematical occupations, according to the Bureau of Labor Statistics.

The additional risk may not be right for some people (some people want as close to zero risk as possible), but again, that doesn't mean that there is anything inherently bad about the underlying mathematical idea of leverage.