The "cash flow rule" (and I'm not sure how you define this "rule") is only one piece of the pie.
More downpaymentreduces loan interest paid and reduces the minimum hazard insurance requirements but It reduces liquidity which is so important in life.
Also, placing a rule of assuming 100% financing is not something to do every time unless you intend to do 100% financing which I don't recommend. Do the calculation based on the loan options you have.
No one house and tenant are alike and despite what it seems, it's a grind to make money on both the front and back end so start small so you can learn all the **** a blog can't teach you.
Keep in mind, the longer you "buy and hold", the more money you will fork out in repairs and upgrades. A brand new Home Depot kitchen today is dated in 10 years. So you may as well add
new kitchens,
baths,
maybe a roof,
probably a hot water heater, maybe an HVAC,
maybe siding and Windows, definitely floors unless you go tile...
to the "cash flow" model if your looking long term or expect to lose in appreciation rates relative to the guy up the street that just sold brand new trendy stuff.
"Less is better than more, sooner is better than later"