My long term is to acquire a RE portfolio that will sustain me and my interest through retirement and also serve as a legacy tool for my children.  

Will the area be economically sustainable in 10 years or will you need to sell out by then.

However, even though it is great for quick money, the only way to make it sustainable is to create a business and hire employee's or VA's, so that the business operates independently.

I feel the need to not just create a successful and sustainable life for myself but put my children in a position to own something that generates a source of income outside of their main subjects of interest.

I’m figuring it out just like everybody else but remember whatever business that you pick - you have to think about the ability to sustain it.

At the moment, I put aside about 40-60k in start up capital to start this new venture and I am wondering if that is actually enough to make this a viable business that can sustain my life and pay all my bills?

It's not sustainable past a certain point, and when I get there my business model will change, but by then I'm sure I'll have hit my modest financial goals anyway.

A more precise way to word this would be that a primary residence does not generate cash flow upon which one can sustain early financial freedom. 

I would then pull out the equity and use the cash for another deal.This strategy worked well but I found out that it was not a sustainable way in growing my personal portfolio.

The CoCR is only as good as the ability of the property to sustain it.