To pay for this, I used a heloc on my current home.

Pay your attorney and your CPA for a customized advice. 

If I sell one house per year, it will pay for itself.

The struggle comes when you plan to sell, pay close attention to how the bank would treat the loan in the event you would sell.Even though its a bit more work, banks are typically open to these loans as it provides them with additional collateral in the event of default.  

Just sell and pay off that loan or two.

What should I do if my tenant isn't paying rent?""

In fact I can have half of the rooms occupied and still pay the mortgage. 

Now, you need to figure out how to find deals and pay for them.

Owning a duplex at 20 is a huge accomplishment, and it’s inspiring to see you’re already planning your next move.From my perspective, real estate investing is a long-term game focused on building equity, paying down debt, and maintaining stability over chasing short-term cash flow.

I currently live in a 1000 sqft home that we pay a mortgage on.