Some lenders do not withhold any retainage.

We also set up milestones for larger projects so they know they will get paid certain amounts when certain tasks are done, but always withholding a large chunk for the very end.

One report I saw said that something like 80% of the ADUs built were to house parents/children of the homeowner and were not being rented out.

The court forms do not track this type of eviction so based on your sophistication you may spend a considerable amount of time and if you are off in the slightest the court will withhold judgment. 

You know, I don't know what my parents paid for it back in 2004 (ish). 

Set up an LLC in the property’s state for liability protection, and consider a parent LLC if needed.

With a natural in and use owner occupied housing, you could likely end up with 1-2 houses a year (each in a new city).The other option is when your baseball career is over, you will most likely end up back in your home town, so you could start the brrrr process there with maybe your parents checking in on the work the contractors and property managers are doing.Best of luck.

Owning properties through LLCs in their respective states avoids the need to register a foreign LLC, which adds costs and administrative requirements.If you plan to acquire properties across multiple states, you could create a parent LLC in Florida and have individual property-specific LLCs (child LLCs) in each state.

In a few of the states there is either a form. you must sign or an application that your escrow closer must file in order to exempt from any state taxes or withholdings that might normally be collected at sale . 

The tenant may be setting you up, hoping you don't respond so she has a reason to withhold payment and take YOU to court.