I'm trying to ruin a scammer's day (fake check scam).  I have his phone number. I am able to call (and record) and text him. He is also willing to mail items to my house. What can I do to find out more about them using social engineering or through service providers? How might I be able to build a case against him, or scare or stop him from continuing scamming people?

I know I can call the FCC to report it, but I feel like that won't do anything. I also understand that I likely wont be able to get very far in following his trail.

Inform law enforcement.

You can't "build a case" because as a layman you likely have no idea about proper police procedure. Most evidence you collect will likely be inadmissible in court. You might in fact also break laws while you collect evidence (for example, recording phonecalls without the consent of the other party can be illegal in some places). 

Attempting to scare them is a really bad idea. Remember that you are dealing with a criminal. That criminal might be violent or have contact to violent criminals. So when you try to intimidate them, they might turn that around and start to intimidate you instead.
