NONE, not a single darn time has ANY of them done it legally/correctly.

A flip, single family rental or small multi family rental?

As big as you are, you should consider moving the properties into multiple LLCs (my personal rule is no more than $1M in single familys in one LLC, but this may need to be higher in your area). 

Purchase price: $255,000 Cash invested: $100,000 Single family residential home in A Class neighborhood.

Thank you again for your response and insight.I have most luck utilizing the local MLS for minimum 6 month leases under furnished rentals  

Meanwhile pay little or no taxes utilizing depreciation.

A hands-off garage conversion ADU is over $100, even doing much of the work yourself, it will be much more expensive than your estimate.Single ADU additions in single family zoned areas are typically one of the worse re investments. 

Maybe concrete single-family 1-4 units depending on the price point and cash flow.Also there is no real MLS in Puerto Rico you need to find an agent for each area you want to look at.

Each property has two savings accounts - security deposit & reserves, and one checking - mortgage payments and utilities 

To clarify my previous post: 80% LTV is available on single family homes, 75% LTV is available for 2-4 units.