When your rental income is 1.5-2x the mortgage payment - as is typical for highly refined STR strategies - they're basically not concerned about the mortgage payment.

Basically, more than a certain amount of STR and MTR in the same building were considered a hotel and I would have had to have 24/7 staff on site.Were you able to get around that with the local municipality?

If a sponsor resists this basic transparency measure, consider it a serious warning sign.  

According to Warren Buffet, Fannie and Freddie really failed because of high-leverage risk-taking in the fixed income arbitrage space, saying:“The portfolios are what really got them into the trouble…the managements of Freddie and Fannie tried to juice up the earnings, basically, because the insurance guaranteed that they were given that mortgage.

Most will require basic documentation such as a complete loan application, ID, Entity Docs, and 3rd party contact information.

That is the basic run down, I would suggest syncing up with a real estate knowledge accountant for your specific situation! 

Please note the information provided below is a layman's definition designed to provide a basic understanding for the general audience.

@Nathan Gesner  is on point yet again, start with your basic estate plan first just like he did. 

Can you arrange for counters, floors, painting other “basics” without him tacking on his 20%?

Typically, you can only do one rollover per 12-month period (again, IRS Publication 969 has the details).In the end, having the option to invest your HSA funds is usually a better bet than letting them sit in a basic savings account.