I want have a 120% of my income coming from passive income sources, as a buffer for life's unplanned events. 

I don't know if that's the best formula, but it's enough that I could pay for about any $5k unplanned emergency at any of my 4 units, plus a couple months of the full mortgage without any rents being collected.I do have access to other money of mine if an even larger catastrophe came up, but the 6 months is what I keep on-hand, at the ready, for those two properties.

For the HVAC I would have it cleaned by a professional company, make sure to have the ducts sealed with a smoke sealer product and they thoroughly clean the heat exchanger coils and squirrel cage blower.

That's because you aren't available or willing to take the calls on Christmas about a plugged up toilet, the guests are stuck in the snow, or there is a squirrel in the fireplace.  

To un-squirrel my day, I made one of those things I mentioned earlier.

If I am diligent with my spending (not easy to do with 7 kids) then I could squirrel away 3-4k per month with my W-2 income.

We found piles of feces from a variety of animals, more mold than a cheese factory,  some insanely disgusting mattresses, and 1 very long-dead squirrel. 

Below is a brief description of each risk item.EvictionOne of the largest unplanned expenses you may face is evicting a non-paying tenant.

I am looking for a pest removal company to remove a squirrel from my attic as well as patch the hole where they are entering from.

I'm more of a grey squirrel type investor, wanting lots of streams in case one or several go bad.