Great 4 bedroom 2 bath family home that we sold for a great profit.

After expenses, which included a special HOA assessment and a month's rent to my agent, 24 payments of $1595 ($38k) left ~$12k in rental profit.

Currently own one duplex which we lived in for a while, but are now renting both units with a nice monthly profit. 

The profits would then get re-invested into the next home and continue the trend until I am able to able to build the next home with the profits that were made from previous sales.

You will, basically, be starting a flip from a negative equity position, and you'll have to dig out of that before you can turn a profit.

In my opinion, getting these right is the primary concern.There are several ways you could structure the finances and profit split between you and your partners, and you'd probably want to consult an attorney (on the structure and terms) and CPA (on the tax implications).

Iam getting into rental property and for my first house should I put my profits toward the mortgage to get it paid down quicker?

Subtract that basis from the $15000 and that will be your profit. 

Churn is the frequency with which you lose tenants, either because they want to leave, or because you're forcing them to leave through an eviction process churn is the real killer of profit and is not covered as often by BiggerPockets or other forms as it should be, in an area such as st.

This current BRRR will actually profit about $350/mo positive cash flow after all expenses including holdbacks for vacancy, repair, capx, etc.