I tend to think that BRRRR has been so popular over the last decade because prices have been increasing and rates have been decreasing, acting as a HUGE safety net against thin deals. 

So I just want to arm myself with as much  knowledge as possible and make the right call. 

Also, if you have a HELOC, those can act as great safety valves if you have a temporary liquidity issue. 

Then you screw in little bracket arms into the stone that also hold the sink up against the counter.

The only issue I see here is that some lenders will consider this a non-arm's length transaction and may have an issue lending on it. 

I have read David Greene’s book on long-distance real estate investing, but my guts tell me that it won’t be that straight-forward as outlined in the book.I think the sweet spot are properties that haven't been fully rehabbed, but that have had structural, safety, mechanical and are updated cosmetically enough to keep the tenant happy.

It was purchased on a 5/1 ARM at 3.875% about 5 years ago and started out as an accidental house hack due to a temporary out of state work assignment.

I also own another duplex- Commercial loan in the name of my LLC- 20 year amortization, 5/5 arm @5.75%. 

I've done dozens of FHA deals, and as long as your property has no health/safety issues, adequate electric service throughout, decent roof, solid siding, handrails where needed, no cracked walkways, no termite or carpenter ant damage, you should be ok. 

Take care for your own safety and that of others.Good luck!