If we were to sell this property in 2019 we are under the impression that you will not owe capital gains on the profit if your taxable ordinary income is less than $77,200....?

It is about 100 dollars in profit.

You can not profit from the proceeds of the Solo 401K.

Rents in that area around $1200/m after renovations but when I look at the math, $14k per year in rental income with about $8k a year in taxes and insurances (not even mentioning maintenance), which doesn't seem too profitable.  1.

I'm here to learn and to develop this understanding into something profitable and long-term. 

I know after this I have no profit, but the tenant is paying the majority of my Mortgage, taxes, and insurance. 

You're not only losing money from cash flow(-), but you're losing potential profits from an investment that wasn't taking away your profits...and your seed money at the same time.Those profitable returns you're losing, is (should be) exponential. 

As an example, for a 20 unit apartment building we would need to hit $100 profit per door per month after debt service to hit our yearly cash flow goal.After purchasing the fifth business (year 6) my business partner would retire and keep their half of the yearly profit (~$60k) and I would switch from adding new businesses to using the snowball strategy to pay down the debt on the 5 businesses.

Key is to clearly define the partner obligations and profit sharing, etc.

Even if the profit margin is smaller I'd rather hit many singles than hit a single home run.