My BIG dream is to build a portfolio big enough so that we can replace our current income and retire comfortably (dream big they say, right ;)?)

The walls will likely have to be primed and painted as well once they're out so it's an additional liability. 

You use Sch E to report your rental Income.

Generally, the spread to account for the higher risk has historically been around 170 basis points (or 1.7%); however, in the last few years, this has ballooned to around 300 basis points (or 3%) amidst lots of volatility.Without delving too much deeper into the math and financial fixed-income calculations, mortgage bonds generally have yields or returns based on the main alternative for note investors, which are U.S.

Income-expenses. 

Consider adopting a split-unit rental approach to increase your rental income by renting out the upstairs and downstairs units separately.

You could use some of the rent collected in the duplex to increase your income basis.

One area that has caught my attention is the Pigeon Forge/Gatlinburg TN area - seems like there is a good rental income to acquisition cost ratio.  

The only adjustments I made were adding a couple additional rows of data at the very bottom of each page to track what I paid in principal each month, and what my net cash flow after that was.

However, they are proposing dissolving that partnership and allowing original investors first opportunity  to participate in providing an additional 22% of our original investment, speculating a hold until 2026 with a 202% return on the new funds, resulting in a "blended return" of about 36% total return of our original+ new invested funds.