I would also look at Dave Linhdal's book Multifamily millions and Sam Freshman's Principles of Real Estate Syndication.Go to Kim Taylor's site for a lot of good information. https://syndicationattorneys.com/blog/

I have paid down principles in the past but ended up refinancing to get more money anyway.

ahah@Deangelo Washington My favorite principle is called OPM, which stands for Other People's Money and is the key to scale quickly.

Keep in mind you will ALSO be paying principle in each payment...

Principles of real estate syndication by freshmanIt’s a whole new business by trowbridge

They think that by removing long term renters from homes and reducing housing stock it has significantly affected the rents and caused homelessness.I believe in free market principles. 

Paystubs have worked well for us.We usually only run a background check to verify what we already seem to know - we cover the basics in the interview, but we follow the trust, but verify principle.

Let's say your interest rate in January was 4% interest only for 10 years and then interest and principle for 10 years and it adjusts every 6 months.

In principle I don't see why you can't do this, as long as all parties know what's going on.

It does require a little creativity to initially setup since YNAB is really built for personal finances, but the principles of zero based accounting and giving every dollar a job (budgeting categories) make planning for expenses so much easier.