I am thinking three apartment buildings (professionally managed Class B/B+, Cap Rates 7+, 95% or more occupancy rate) each located in a solid neighborhood in a separate city in NW Washington (one in Seattle, one in Bellevue, and another in Olympia or Tacoma).I wouldn’t need to derive personal income from these investments, as I would put all profits into servicing the debt more quickly and/or investing back into the buildings.I am somewhat nervous about taking on such a huge amount of debt, though, even if the down payment does afford some cushion.

As far as your HELOC goes - you'll also need to factor in how much you're renting out the other sides of your planned duplex and how much of a 'cushion' you will have with that.  

Have a small cushion for emergencies.

I have a good monetary cushion (don’t want to say the amount, but it is more than enough to live on for at least a year without a paycheck) that I plan to use to get settled and begin investing.

I don't care because of many other intangible returns I receive.Folks who buy a personal residence or invest in real estate for appreciation are speculating, to me.When one buys real estate for a significant discount one has a built-in cushion.

If you can take out the cash and can still have a safety net/cushion I would say use the cash vs pulling out a loan for a lesser monthly payment. 

This would give you a cushion, without having to pay interest on it.  

Congratulation good job on your deal, the goal is to profit as your buying property. just be careful the banks are known to give high appraisals give yourself some cushion in equity

Personally, I think smart investors have a cushion and plan for the worst, which means being careful with leverage.Your basic math is correct - if you want to exclusively use the BRRR strategy to live off the passive income in the short term, you're probably looking at 50-100 doors in most markets.

ROI is better and will have more cushion.