Rent is below market rate for the general area.

As I'm sure you're well aware, the small multifamily space in metro ATL is competitive despite current interest rates. 

At CA tax rates it doesn't take much to be a significant number!  

I offered them 10% down, interest rates favorable to me, amortized for 30 years, but with a balloon payment after 3-5 years.

my experience has been (1) I can obtain the same rental rate for a 6 month lease that I can for a 60 day “stay” if FULLY furnished (2) some of these 6 month rental turn into 2 years or more.  

Quote from @Sean Kirk: I'm seeing what seems to be 10%+ cap rates on roofstock.

Private Money or Hard Money LoanHow it works: Short-term loans from private or hard money lenders to purchase the lot and finance the construction.Benefits: Easier approval and faster processing, focusing on the property value rather than your income.Downside: Higher interest rates and shorter loan terms (typically 6-18 months).

I am now 29 and wanting to grow at a faster rate- and also ensure that I am making smart moves, rather than just grasping at whatever a bank will give me.

Working to figure out which route has the best conversion rates when targeting specific neighborhoods.

I would say anyone who has done 5 flips is experienced and that success rate should be closer to 90% and up.