Beyond that- is the population in the area growing or shrinking?

There are not many people who are disciplined enough to save at the rate you have thus far.In this business both short and long term you either need money or access to it to grow and sustain, there is no way around that. 

If you are real and looking to grow but not for a handout you will be surprised by generosity.

New with the four Tennant's and raising rents 25$ it would pay for itself with lots of room to grow which it has.

If you are going to grow your rental business to any significant size I think it is worth learning and using it.

Strong equity that grows while it pays down several hundred per month.

I currently have several sfr props in Texas so would like to stay in the same growing state.

So if you like this type of work, you will have to grow your business to more units in the long run.Keep in mind, multi-family buildings are probably at peak pricing these days. 

If your family grows sufficiently in size that the current home is no longer suitable AND your current LTV based on a new appraisal is below 75%3. 

Also want to add if you domicile in a market with no real appreciation.. and you dont have a job were you can hit big homes runs.. then growing a rental portfolio or fix and flipping is to me the best way to grow your net worth.. with the idea of at the end of the run retiring as much debt as possible to end up with free and clear assets or nearly so.