I much prefer Rome to Paris, so I applaud your taste, but Paris can be fun too - depends how much time you have.
French food is great! Anything with a chicken or bean base is likely to be well flavoured, well cooked and reasonably priced away from the main restaurants. And yes - DO have moules frites et biere (which you will be able to drink if accompanied by an adult)
Parisians don't hate Americans - they hate everybody. If you work on that assumption, you'll be delighted when and if you are greeted with courtesy.
How's your French btw? Things will be much easier with basic reading and listening skills, but it's not necessary to speak it - in most places your French will be viewed with derision unless you're very fluent, so my advice is play the ignorant foreigner and point
Don't mess about on the Metro. Two friends of mine when I was in my teens were "arrested" for general horseplay. They were probably behaving like idiots, but nothing that would have come to the attention of the authorities in London. They had to present their passports at a police station and were given a talking to. I wasn't there at the time, but I know it scared them rigid. It was a while ago now, but I can't believe security has relaxed in the current global situation.
I agree with breakingnews 100% - if it's at all possible, go to Montmartre (if you want a flavour of what it looks like before you go, watch the French film Amelie)
Finally
read if you want to get the most out of it. Get a good guide book and decide what interests you and what you want to see. There are hidden gems everywhere, and only you will know what floats your boat. Above all - enjoy