Has she even received a supplemental tax bill yet? 

Our portfolio currently cash flows, but cash flow isn’t our top priority right now since we plan to use this portfolio to supplement our retirement in 12 years when I leave the Army.My biggest challenge is committing to an out-of-state market.

With that in mind, I’m considering purchasing four rental units over the next four years to build a stream of income that could help supplement my retirement by age 68.The challenge I’m facing is that the deals I’ve come across so far don’t make financial sense.

- The market is in a little bit of a lull right now (buyers market), its a great time to buy, but slower time to sell (my primary business is flipping houses) I can supplement my flipping business by providing project management services/consulting, helping investors find discounted properties, etc. etc.

A bit about my situation and motivation for getting into real estate investing...I have a full-time, high paying W2 job as a specialist physician that I generally enjoy but would like to  be able to supplement my income over the next 8-10 years if/when payments decline in medicine.

How they could be more intertwined and supplement each other. 

I also helped my mother get 2 rentals to help supplement her retirement, mistake #1b.

It's an estimated cash on cash return given current rental rates subtract expenses assuming 7% interest rate, 10% management fee, 5% repairs, 5% capex and other expenses like mortgage, insurance, tax. it's a estimate to tell you what properties to analyze vs ignoreyou can see the are pockets of negative returns as well as pockets of positive return. this is to supplement the data @Devin Conley provided

Unless there is a history of STRs in the property already and you have experience with STR, you really wouldn't be able to supplement your income with that. 

It's not quite as easy as renting out two sides of a duplex, but with the right marketing and management you could rent out the extra unit to supplement the mortgage payment.