We should fight it, to be honest.They want to convince everyone it is inevitable to shove their damn technology down your throat. 

You may be able to get away with 10% down if you have multiple fix and flips/holds completed in the last 36 months and the LTARV allows for it. 

I even looked down on single family home investing.

My ultimate goal is CASH FLOW (comp rentals $4200/month).Doing the deal cash provides the most cash flow but I would like to BRRRR and recycle that money into another property down the line and grow my portfolio.Thoughts?

If it's down payment towards another property, then a HELOAN is usually better suited than a HELOC. 

Let's say I house hack by putting 3.5% down through an FHA loan.

They say it might be a tear down...who knows...Building in the area is pretty high.

That $15K would have to be enough for either a 3.5% down payment using FHA for example and lean heavy on the seller for a Seller concession (Seller credit) which goes towards closing costs.

If those things go down the values will go down (or rise more slowly), like in the rust belt.And keep in mind you're on a forum full of RE agents. 

I would also research closing cost and down payment assistance options, the more equity in the house you want to purchase, the more likely the bank is to approve you.