The difference between the average daily balance of the HELOC by depositing ALL your income into it - and using it as a checking account is what does the trick.The fundamental mathematical principle is not "paying extra on principal" it is REDUCING ACCRUED INTEREST - which results in more money going toward principal. 

So I think VISION and ability to adapt to plans are key fundamentals to this successful partnership. 

A good market for passive investors in large commercial multifamily deals might not be a good option for a new investor looking to do its first small to mid-size active multifamily investment.With that in mind, there are still a few fundamentals that need to be looked at regardless of your investment strategy.

Many HOAs encourage this as a fundamental of good neighborhood security, even in already very safe areas.

It's also dependent on your role of active vs. passive, how much capital you have access to, and what role you're looking to do.Either way, for fundamentals I'd recommend:- Buying Real Estate Without Cash or Credit by Peter Conti and David Finkel- The Landlord's Survival Guide: How to Successfully Manage Rental Property as a New or Part Time Real Estate Investor by Jeffrey Taylor.

All of those fundamentals got me intrigued for the probability of low vacancy and potential to raise rents over time. 

PERPETUAL BULL MARKET irregardless of fundamentals, P/E, economic outlooks, unemployment, deflation/inflation, debt, bond rates, etc...

But over the long term, in the aggregate, people are generally rational, and the economic fundamentals underlying all of this are pretty simple.

You have to buy on fundamentals and not factor in much appreciation if any save for what might trend with inflation.The big question is if you buy something now and its on par with what you are paying in rent then thats a push and you have all the benefits of owning your own place, both psychologically and economically, if you are buying for speculation of it going up in value I would discount that.

It's like asking a pro athlete how they do something, the answer rarely goes beyond fundamentals and clichés.