I've got about $525K in equity in the property, but lenders have told me that I cannot get a HELOC to access that equity for additional purchases because the duplex was financed as an investment - they have said TX law dictates that HELOC can only be used on primary residences.

You need someone with boots on the ground and someone who has done this before.

You can always purchase more and take on more debt. 

You don't need to learn REI in your job, that's a side thing. 

These areas tend to have more affordable properties compared to central Phoenix and still offer strong rental demand and appreciation potential.

Even at $2200 I don't expect to get a positive cash flow for the first year, but that's okay as long as I rent it out and learn from my mistakes for my next investments.

I see many situations where one generation wants to buy out a prior generation or, more typically, siblings.

10) Knowing what to do if tenant is late on rent or doesn't pay.There's a lot more, but many here on BP self-manage and learn via "trial by fire".Of course, you can always hire a Property Management Company to handle it for you.

None of this has anything to do with your personal tax return.

I have flipped new homes and townhomes but phased out raising a family and now am focused on utilizing my skills which are building, selling, expanding a circle of influence to focus my effort on the above.