If the down payment that you need equals the entire 70% to 80% in value of your SFR, then I would go with the cash out refinance and get a fixed rate.If you only need 20% of the equity for the down payment, can pay it off relatively quickly, and want the rest of the equity accessible for future use, go with the HELOC.  

The standard solution is to exchange the land for some other investment real property - anything from another land to residential or commercial rentals to a completely hands-off real estate investment.

Depending on the condition and location of the property, the cap rate in your area may be 5% or 6%, but ask a local realtor that does commercial deals.

I really like the fact that you can easily have access to your documents via all your Apple devices.

For the loan, I would plan on talking to commercial loan departments at various banks since you have 6 units. 

I currently have a few SFR's and MultiFamilies and have them all on commercial loans from 5-6% interest /  20 year / adjust every 5 years. 

RealtyShares - https://www.realtyshares.com/ - generally focus on mid-market (<$50 million) commercial properties, often for value-add situations involving property upgrades or operational improvements.

Affordable prices and booming economy and GROWTH:The region has been Virginia’s fastest growing for five consecutive years, with a population of 338,000.A highly skilled and expanding labor force of more than 1 million resides within a 40 mile commute.Strategically located just 35 miles south of the nation’s capital and 35 miles north of Richmond, capital of Virginia.Over 47 miles of Interstate-95 serve the region, carrying 120,000 cars per day.Excellent rail service is easily accessible, including Virginia Railway Express’s commuter service and Amtrak.

I currently have a commercial loan on the property as I never lived in either one but have completely remodeled and rented out both. 

@Jay McCreary as veterans we have an awesome opportunity to use the benefits of the VA Loan to begin our real estate investing journeys much more quickly and effectively than those who do not have access to VA Loans.