Can I meet my friend during a connecting flight? (LHR)

So I am traveling to Paris from NYC, but I have a layover at Heathrow for about seven hours. I wanted to meet up with one of my close friends during the layover. We are not going to leave the airport- we just wanted to grab a bite together in the terminal (pre-security). However, I have a few questions about this and would appreciate if you could leave some advice for me.

Flight info: JFK to LHR --(seven hour layover in LHR)--> LHR to CDG. All flights are under British Airways.

1) I am a U.S. citizen so is it possible for me to meet my friend without buying a visa?

2) When I get off my flight and arrive at Heathrow, do I have to go through the "connections route" or just through the "arrivals route"?

3) If I do end up meeting my friend, do I have to go through security again?

4) Usually how long does it take to pass through security, customs, etc. before arriving at your gate for the 2nd flight (LHR to CDG)?

5) Do I have to pick up my luggage from the carousel or do I just leave it, since it'll be going to the final destination?

6) Do I have to convert my money to use when I am outside of security (pre-security) if I want to buy a meal? Or do they accept USD?

Thanks in advance :)