I am helping the buyer buy allowing him to buy it and not listing it on the MLS.

There are plenty of programs out there that will allow you to create a state-specific lease with all of the required language for your state and will also let you modify it to add your own special terms, like your parking requirements, quiet hours, how trash and utilities will be handled, etc.

This would allow me to have smaller payments on my primary residence.

Essentially, it allowed it me determine the exact neighbourhood in Phonenix where there is a ton of demand for vacation rentals, and also helped me find the exact type of property to buy (including amenities). 

Buying vacant allows you to choose your own tenant and make sure you're getting market rents.

It's not the best but it is a lot better than most of the Free Real Estate softwares I have seen, but this is because I make sure the software allows me to create Journal Entries, in case adjustments need to be made.

If your situation allows you to go elsewhere I’d start looking for more favorable markets to start in. 

The way that I did it was pulling the equity or doing multiple cash out refinances at the same time in 2021, which allowed me to accumulate almost 300K in cash.

There are some exceptions that allow for pro-ration such as military orders and change in job location.1031 exchange isn't possible since thats only for investment property. 

Although, you're not going to find much under $100k that allows STR.