I helped 37 clients buy or sell multi-family last year and in my experience from these and many other is that those people who want to build wealth and supplemental income through rental properties usually struggle the most with saving the next down payment, which is the true value of these live in loan options at 3.5% (FHA) and 5% (conventional)..  

They are going to be supplements to other steams of income in my retirement.  

I own a primary residence on Maui and am interested in building an ADU to supplement income after losing my vacation rental condo in Lahaina.

And typically it's in conjunction with other activity such as grazing cattle, growing crops, timber, etc.I can't see it being a good way to make money, just a supplement to farm/ranch income.

I have my Masters degree in Project Management and my retirement plan is to have enough rental properties to supplement my W-2. 

Tenants should be paying market rent otherwise their landlord is supplementing their rents.

Capital gain and rental income are not our main investment objective but it would be nice to supplement our living expenses.  

We are hoping to own several single family or multi family properties in the near future to supplement our cash flow in order to gain financial freedom and be able to retire early, travel, and not have to worry about a "9-5" job for the rest of our lives.

I'll try and supplement @Rick Stein's thoughts since what he stated is important, but many of us have a hard time accepting it without some perspective:When going into a vacancy/tenant screening situation its easy to get anxious about the dollars going out day by day.  

If anyone has any recommendations, that would be great so I can supplement what I find and hopefully discover some things I couldn’t find.