You need a loan not secured by collateral or something based on the new property. 

The first home secured the LOC, the second home secures the addition because once you pay cash it is free and clear. 

Don’t touch the security deposit until she moves out.

Long story short, I paid off the loans with the lines of credit, which I continue to utilize over and over again for the same purposes I've spelled out for you.There are other methods and if you'd like to message me feel more than free to do so!

Otherwise, you should be able to go up to 10 loans through conventional methods.

What is the most conservative methods for tapping into the equity and slowly building my property portfolio.

It's simple: He complies with the payment dates and method detailed in the lease or you move to evict him.

Or should I go with just getting 2 or 3 secure cards  to start building my credit and ignore taking care of the debt (credit score-610)?

My goal is to use the BRRRR method and have at least 11 more rental units (either SF or small multi-family).

Its important to note that the rent from the 3 units is added to your income to qualify (less advantageous calc method)  and is not used to offset the mortgage (more advantageous calculation).Also you have two current loans outstanding VA loans that have 67% of your 667k limit tied up.