I'm not sure if this significantly alters the zillow quote.  

Some allow you to change code with app so others cannot re-enter.

The whole aesthetic of the property changes with a few minor alterations.

Pick one zip code, or one neighborhood and a specific type of property and focus on that for a while. 

I can't recommend any books, but for foreclosures and tax deeds, a good place to start is to get all the info you can from the sheriff or court house clerk who puts on the auction, and read the state's revised code/statutes on the subject.

I am currently finding a property, then staring at various maps and essentially guessing as to where it falls, then researching codes and regulations in that area.

Make then register a phone # and text a confirmation code, get their IP address?

We've removed a lot of K&T over the years due to Insurance mandates & code requirements.

When building a duplex and i'm the GC do I need an engineer to be involved or can I just get by with an Architect stamping off on my plans and making sure they are up to code? 

I am not allowed to broadly advertise specific commission rates; however, I am allowed to mail postcards offering special commission rates to areas where I've recently sold or if they give me permission to target a specific group (like non-owner-occupants in a specific zip code, for example).