Btw, this kind of note-taking has been extremely helpful in other aspects of my life, and I imagine it will work quite well for real estate as well. 

Verifying last 2 years of rental history and income extremely important to find the “best of the worst”.Make sure you understand the Class of properties you are looking at and the corresponding results to expect.

Even the most expensive property managers are EXTREMELY cost effective if you really think about it!

It is extremely odd the previous companies did not ask for that if they are collecting rent for you and issuing you disbursements.  

I use it for my rental property extremely easy to use.

Self-showing services are extremely common but that should be in the contract. 

Go to Etsy and search for "rental property tracker," and you will find hundreds of nice spreadsheets to track 10-20 rentals, usually for under $10.Software has extremely helpful features like online payments, marketing syndication (click a button, and your property is advertised on multiple sites), electronic document review/signing, maintenance tracking, and owner reports.

Wholesaling teaches you an extremely valuable skill in RE: How to find off-market deals.

I was extremely humbled by people and their excuses when it comes to paying rent on time.

In 1997, I don't fully understand why, the City of Denver paid the golf course owners $2mil to rezone this parcel as a "conservation easement" this was extremely restrictive zoning and meant it would essentially be destined to be a golf course for eternity 3.