There are quite a number of things that can make utilizing an FHA loan more difficult such as more barriers during appraisal, appearance of low qualification/little cash, typically longer closing period, likely higher interest rate, and PMI cannot be dropped without a refinance if 3.5% down.That said, just chain 5% down conventional loans, and make sure your duplexes pay for themselves.  

There are a few strategies you might consider to accelerate things.One option is a cash-out refinance.

:)  Is it still cash flowing after the refinance?  

You have used home equity lines of credit to purchase investment rentals and want to know the best way to pay down the HELOCs.Between the two properties you bought, after expenses, you have $250 a month positive cashflow to use.What I like to do is pay down some principal every month with my positive cashflow.I use my extra active income from real estate commissions helping other investors to pay down the principal even more which just frees up that credit for me to use again.I know I can refinance the HELOC debt before it changes to principal and interest as it is just interest only payments as yours are.One difference is the cashflow, I have greater positive cashflow and could make the principal and interest payment in the future with the extra cashflow I already enjoy.I always get HELOCs on my income properties as well after purchasing them to pull out as much of my downpayment as possible.

my condolences on your recent lost.there are a few ways you can do this, as mentioned above you can take a heloc on your primary residence which will give you a second mortgage, first mortgage payment wont be impacted. you can do cash out refinance which will give you one mortgage and payment. it will pay the old mortgage and give you money in your pocket to pay for the rehab.or you can do a renovation refinance which is similar to cash out refinance but we would contractor involved  as part of the refinancing and they are paid through the loan

Focus on wholesaling the leads I get from my campaign (while refining my underwriting and acquisition skills) to stack up cash, then begin acquiring rental property.2.

I’m a full-time sales professional at a global GSI, so I’m seeking relatively efficient strategies.Has anyone successfully used cash-out refinances, 1031 exchanges, or other equity-based approaches to boost income?

Find a good agent who can write a vacant/builder's risk policy, then during the refinance have them switch to a landlord/fire dwelling 

@Brian Chadwicktry a cash out refinance. 

Sounds like a cash out refinance would be the best way to tap into that equity.