I'm assuming you're at Shaw AFB, so I looked on the east side of Columbia and this is the lowest priced duplex currently on the market: https://www.realtor.com/realestateandhomes-detail/7037-Julia....

Let's assume you accounted for all expenses and have a full $2,400 monthly cash flow.

My preferred options are:1. house-hack with a duplex under ARV; live in one unit => renovate => rent the other unit2. buy a SFH under ARV that could be converted into a duplex (preferably adjacent units vs top/bottom) - I'm assuming the biggest challenge with this strategy would be separating the infrastructure for utilities; and costly.

What type of properties are you looking to add to your portfolio, I'm assuming SFRs, is that correct?

The problem with vacancy is it assumes all products are the same, our 2 bedroom which is designed much better than our 3 bedroom and more thoroughly remodeled has lower vacancy.

I assume you're doing this in/around F'ville?

I would consult an attorney who specializes in this.Also, assuming the property is in California, if it wasn't subject to CA Rent Control, once it goes into the LLC, it might be.

Selling the investments, paying the capital gains tax, and paying off the mortgage would save you $91,356 over 30 years.But...The total appreciation of $172,500, assuming an average stock market return of 7% annually over 30 years, would be approximately $1,313,114.  

You can assume about 1% in closing costs in addition to commissions so you're starting around 7% before the seller gets any cash at closing. 

Assuming you don't plan on going back into any consumer debt again I like your plan versus barely getting by.