Selling rental to pay off primary?

[Nolan Romero]

I'm just starting out. Trying to find my way still. Not sure what kind of investing i want to dedicate myself to.  I have a rental in southern CA that pays itself,  but no extra cashflow. I can sell it and pay off my current mortgage with the recent equity. And save up to buy a rental cash in a few years. My current mortgage only has about 7 years left , but my rental still has 27 years. My goals are to have a few paid off houses when i retire (about 17 years). Any advice for a newbie would be appreciated?