So, my question is what articles are essential in a real estate investing business?

The property is in good school district and the houses around it are significantly priced higher (~20% higher).

There are dozens of other factors in your criteria but you get the point for multi-family.If you're doing single family look for areas that have good school districts, large populations, high list-to-sales price ratio, low days on market, path of progress, etc...You don't need algorithms.

I have seen newly rehabbed homes which, essentially, needed to be gutted and redone--a much more expensive process than the original rehab should have been.

The Sewer District requires a notarized letter to move the bill into a tenants name, I have basically been forced into including it in rent (and eating the 5-10% increases every year).  

Essentially, an agent has 'insider' information that a listing has expired, they can't use that knowledge to solicit them.I'm currently only targeting FSBOs.

It depends on the school district.

About 2-3 weeks later we mailed Yellow Letters to that same group of owners and our response rate essentially quadrupled.

These are essentially tethering kits that are installed behind large items of furniture to allow them to be "tied" to the wall.See this:http://www.nbcnews.com/id/48573739/ns/health-child...These kind of accidents are horribly common.  

The advice, forums, and podcasts have been essential for me becoming an investor.