I believe the coupon number is if you heard about the game from an add in a magazine or somewhere else. I don't know though, as when I first signed up, there wasn't anything that said coupon.
As far as H2H, it is free. I have never tried it, so I don't know how it works. If you want to play in the main arena, you can use your two free weeks and try it out. Like Blueice said, I would practice a bit before logging in for the first time. If you can't wait, there is a Training Arena and a new trainer function in the MA. If you do log on, you can often find someone that is willing to help you.
The best advice that I can give is this: do not get discouraged. At first, you will get shot down a lot, no matter how good you are offline or in another sim. Aces High is a lot different than many of the sims out there and there are guys in the game that have been here for 2-3 years. It is a very fun and very addicting game/sim.
Don't feel bad about asking questions, that is how you learn! Also, some of your questions may be answered in the help file that is on the downloads page. It is a Windows Help File and it has a ton of valuable information. You might want to look it over a bit. It is as close to a manual for the game that I have found.
There are also several websites run by players here that have tons of information on how to fight in Aces High and be successful (and this stuff ranges from the basic to the advanced).
Hope this stuff helps and feel free to ask questions!
Hopefully, we will see you in the Main Arena soon.
-math