Your first step should have been to pre-qualify for a Loan.

Go to Etsy and search for "rental property tracker," and you will find hundreds of nice spreadsheets to track 10-20 rentals, usually for under $10.Software has extremely helpful features like online payments, marketing syndication (click a button, and your property is advertised on multiple sites), electronic document review/signing, maintenance tracking, and owner reports.

I am a veteran and want to use my VA loan to house hack a 4 unit, just curios if there is a market for it. 

After a brief search, the IRS says-For tax years 2018 through 2025, if home equity loans or lines of credit secured by your main home or second home are used to buy, build, or substantially improve the residence, interest you pay on the borrowed funds is classified as home acquisition debt and may be deductible, subject to certain dollar limitations.

I'm browsing online listings and want to understand how to dissect these deals before diving in.

My brother's rental is a little over 1,000s sqft heated living area, so the ADU would only be permitted for 500 sqft in Winston-Salem, according to information I found online .One advantage of an ADU I believe would be the ability to hook up to the primary residence's utilities. 

I'm currently weighing my options between using cash from my HELOC or getting a private money loan for the purchase and rehab of a property.

And, since the cash would be debt (you got the money from a new loan), it's not taxable.

There you will be asked your criteria and then after answering a few questions you will be matched with 3-5 agents or loan officers in your area.

Other than that, you will have to use a debt service coverage ratio loan.