Then, if you sell the business after you accumulate say 10-20 properties, you can just transfer account information (email & password).

It's next to impossible to accumulate this many hours.

We would be paid an hourly rate and whatever we  spend/accumulate; the friend would get the cash rent until the differance is paid. 

Due to item 1, adding an ADU can require years to start achieving any return (once the accumulated cash flow recovers the initial negative position).4) Adding an ADU is a slow process.

You have decent cash flow that you'll continue to accumulate, which you could put toward a deposit later for another property. 

You're absolutely right—positive cash flow from rentals can vary significantly depending on factors like property costs, financing, and the ever changing market conditions.For real estate the challenge isn't just accumulating properties but creating a framework that builds net worth more strategically and sustainably.Cash Flow can be generated in many ways, my intention was to better understand the investor mindset and their approach, if they wanted to share.Based on your example, if using conservative calculations at $100K/door, you would pay $20M for access to $40K/month. 

If you kept the property, and accumulated the CF/yr, it would take you 25 years to get that same equity that's sitting, frozen in your property.Also, if you cashed out and used that same equity as a DP on different RE, at 20% DP, that equity would buy you $2M in PV, not just $700k,...and, I'd be willing to bet, you could find new RE that would have a yearly CF well over $20k/year.On top of that (remembering my initial statement above), any appreciation applied would be applied to $2M, not just $700k. 

If you’re looking to build long term wealth, accumulate assets, take advantage of tax code, and benefit from appreciation, then play the appreciation long game.

Meanwhile that guidance pushes many investors towards purchasing in areas where they do nothing but accumulate terrible assets solely because they are inexpensive.

Scale down your lifestyle as much as you can and accumulate good assets to get the snowball rolling down the hill.