what is the overall number of realtors in the US?

Answer 1

It's pretty high. Just as a hint, the single largest brokerage firm in the United States has 35,000 agents alone (that would be NRT, which is Coldwell Banker's corporate branch agency)

I am in a midwestern area of medium size, and my firm has 600 agents. Just chatted with my cousin who is a realtor in St. Paul, and their firm has 2200 agents.

Take it from there.