For me, I obtain high quality tenants, most of which are in services or tech, with multi-year (lower vacancy) automatic escalating rental rate leases based on CPI increases.There are infinite ways to invest and it's definitely possible to increase number of properties while keeping the time and energy managing them to a minimum.I've owned and managed properties in 5 states, 8 cities for over 20 years.

I’m going to make my money back in 2 years based on the cost of me paying for all the heating oil in the multi families I’m converting and then after that it’s an infinite win of increased cash flow every year thereafter.

This diminishes the return and I expect outstanding return for residential RE (typically I have achieved the infinite return via value add/refi). 

But in the installer’s infinite wisdom, they thought using duct tape to hold the overflow sensor onto the pan would be a good idea in 180° Florida attic.

There is no “one” single challenge.Innocent question however until you do a few probates in your local venue do you realize how many variables are involved.How about scaling the marketing side (only) and see what fruits your efforts produce.I’ve done well over two thousand probate transactions since I started in 1978 and I see no benefit to look outside of my home state.We have (58) counties in CA and, despite a single probate code, there are local rules of court to deal with and an almost infinite number of fact patterns. 

If I get a 5k loan, and then put it into the stonk market, then pull out 5.5k, that means I got an infinite return.

Then your ROI is infinite, or beyond infinite if you pull more than your original investment out.

There is no "midas touch", alchemy, or central bank that can expand the supply of either of them infinitely.

I am trying to figure out how to categorize this summarily given the almost infinite number of ways a deal can be structured.

I absolutely love the fact that I can buy a house with cash, in 6 months refinance all of my cash purchase + cash for rehab and maybe even then some back out of the house, and moving forward have infinite return with 3-400 a month net cash flow.