They are reconfiguring it to open concept, where you will reserve an office or meeting room, when you need one.

The tax on Unrelated Debt-Financed Income is not significant, because the IRA will take advantage of deductions such as depreciation and interest on the note to reduce the amount of net taxable income.If you are not familiar with these concepts, get with your plan provider and/or CPA to gain a better understanding.With all that aside, the question of whether to pay off mortgages or not is a basic investing question that ultimately centers around the opportunity cost of the money. 

Investing in Real Estate is such a broad concept, you mentioned the BRRR strategy which is  more specific but could still encompass several sub strategies.

@Jaron Walling Being an investor, I think I was very excited about the concept of purchasing a 4-plex.

I have thought of utilizing them for marketing of distressed properties (driving for dollars), interior demo work for other rehabbers, also the interesting concept of "pre-habbing" that I have read on BP (J Scott & Glenn Schworm), etc.

This is for a completely upgraded (a few years ago - granite counters, open concept, chef's kitchen, great entertaining space, new bathroom) 1 bed 1 bath in an excellent neighborhood. 

It's absolutely insane, but I do understand the time differences, due to the fact that they all pretty much work in the Philippines or Europe.After repeating the same information to representative after representative, and providing photo and video evidence, 24 hours later, they were finally kicked out of our house.What's funny, is that they were the first to provide us with a "review" in our journal on the coffee table....

So one way to think about it is to apply the economic concept of sunk cost. 

Heard the concept of owning your first home for tax benefits and others.

I would have no problem going through the process again and starting from scratch to design and build a multiple unit concept, and engineer it, I just need to know that I will have the finances to back up the build.