On it currently, sits a 4 bd/4bath house (1900 sq ft) that we built in 2018-19.

I asked PM to send a bigger cleaning crew vs 1 person as the house is 2600 and needed a good cleaning.

I found a house in Atlanta that comes out to an IRR around 11% when I run the numbers, is that good or should I look for better?

Which option is better to build a new one or buy an existing one?

The house isn't in a flood zone.

I have been trying to think through how a surging population (via immigration) will impact housing. 

So all in, including some priority repairs we'd want to do aside from the basement, we're looking at about $750k on this house. 

Yes you could buy 1 house cash for $500,000, or you could buy $2,500,000 in real estate with 20% down.When the market appreciates 20%, one would yield you $100,000 while the other would yield you $500,000.This also doesn't calculate the increased cash on cash return you will get with increased rents across all of your properties rather than 1. 

I am owner of my primary house, have excellent credentials, but I am unsatisfied with my passive income and potential to become owner in 20 years of a self financing house elsewhere. 

I don't think listing with an agent will work since I am not looking to sell to the general public, I do get these yellow post cards and letters from "CASH FOR YOUR HOUSE NOW" but I believe those are not investors buyers but more bird-dogs looking to get it on a contract to reassign at closing.