Here is a podcast all about it:https://joefairless.com/podcast/jf392-youre-missing-out-without-condos-in-your-portfolio/ I have a few townhouses that are in a condo HOA and I am quite happy paying the fee and having all exterior maintenance not be something I have to think about.The fee is reasonable but I assume fees in NJ are higher or even dealbreakers.

Base it on what you need it to do.Mine started as a simple (for me...LOL) set of digital forms, that grew into full software...so be careful.

Like an apartment, in small multis you will probably have to manage any common-area maintenance, like mowing the lawn. 

Simple, the savings you get from no interest payments (which isn't a savings to begin with), would have only happened if you reach the end of the mortgage...20 years from now...and, you only get that savings in increments...not in one lump sum.Besides that, it's in the math...you are not saving anything. 

It would be closer to home ownership without the whole burden of exterior maintenance. 

I'm a fan of simple--but thoughtful--physical USPS letters.

Where is the maintenance expense? 

It's not as simple as it used to be.

Are you budgeting maintenance, capex, vacancy, etc...?

nope just do a simple LLC agreement with both of you as managing members or you manage him member and spell out the business arrangement in the operating agreement that is simple no need for PPM if its just you and one investor you know.