Take a gliding path and figure some of the basic puzzle pieces out first. 

I do quite a bit of prospecting and networking with commercial agents to source deals, and find that to be the most important piece of the puzzle.

Two part question
FIRST
I own and rent a 2 family home which has a market value of at least 380k (as of 9/2019, actual by HELOC appraisal properly more now).
I owe 267K on my FHA loan at 3.5% (original mortgage was...

I find this puzzling as to why some investors do both especially when the BRRRR strategy exists.

Less money spent on supplies, less wear and tear on your place, less money spent on utilities, fewer guest headaches, etc.Bottom line: there’s a LOT of puzzle pieces you have to get right to make this work really well, but once you master it, it can be very rewardingI preferred to invest in the year-round high revenue parts of the US where you can earn a lot of money year-round.

The better either of the two numbers (Purchase price below $75,000, and Rent above $1,000) can be, of course the whole thing functions even better.I would suggest the bigger "key" to the whole puzzle is to "buy right".  

The current tenant screening services are just that, "a" screening service which is just 1 part of the puzzle, there is still much leg work to be done and a bit of guess work on tenant track record.

By intriguing, I mean a complicated puzzle filled with potential. 

I understand each of these are slightly different (a PM is a monthly expense whereas a vacancy may only happen once in a blue moon), but to conservatively analyze a property, it seems like the safe bet is to subtract 35% of the gross rental income to save for the reserve costs.However, it seems most people analyze their deals ignoring the expenses that are not from PITI, which makes understanding how something "cash flows" puzzling. 

That's the missing piece of the puzzle for me.