Do I have to wait a couple years so I can demonstrate more clearly that I do indeed have a sustainable business model, or does having continuous income whether it's from my own income or from a regular W-2 job count?

That's just not normal, nor is it sustainable.

Sustainable expense cutting can cut hundreds of thousands of dollars off the amount you need to save and invest for financial independence.   

If you need the money to sustain then the money from buy and hold is slow, it is long term play, so you would then probably want to rehab.

To be sustainable in any market. 

I don't know which ones they are, but rapid appreciation/cost rising without commensurate wage increases (or rabid influx of outside money) won't be sustained indefinitely without a correction. 

But, if part of your idea is for each property to be self sustaining, this might be something to consider.3) Why did you use $180K in cash to outright pay off the 2nd rental in full?

I'm not old enough to say if my plan is sustainable, but I automatically move a set amount of money out of my checking account every month into an investing account.  

My goal for the future would be to own enough rental homes to sustain myself.

There is a risk of getting stuck on any detail be it financing, property selection, taxation or tenant screening (another example: people have posted some formulas so complex and burdensome enough that I am not sure they are sustainable or realistic in light of the recent data that most US renters are financially fragile, (Just Google Financially Fragile Renters, FINRA)...