The second question is what criteria do you use for deciding when it is the right time to expand your model to look at other opportunities that you may not have considered previously? 

The whole financial freedom through real estate movement/model has been created on the back of artificially low interest rates following the Global Financial Crisis and that model won't work anymore for most unless interest rates or real estate prices in the US drop dramatically and most economists think they won't and for good reason.

Doesn't sound like it will be a particularly hard model to copy, and when the word gets out you could find 10 houses on the same block under cutting your prices by 50% or more. 

For the AC, I went with the GE Profile ClearView window AC unit, specifically the 8,300 BTU model which runs off of a standard 110v outlet, and is available on Amazon with Prime shipping.  

I think that he has a very good model. 

There is also alternate rent models such as STR, MTR, rent by room.  

Although the rent by the room model does come with more upfront work, and more tenants to manage.

@Robert Ellis yes we have a duplex model that we build in Lehigh Acres and Cape Coral.

After a quick Home Depot search and a pre-Fourth of July sale I saw a similar model that was selling for $1100.

Don's model is basically what I'm trying to do as well.