Do I have to provide my banking information and agree on the contract(or whatever that is) beforehand, Or should I only do it once it's time to receive the money?( if there is any money at all) and iAds will just start working automatically?
Just some helpful advice, if you haven't started using iAd yet I wouldn't bother setting up iAd. Apple is stopping iAd services, and aren't allowing any more new ads into the network. So at this point if you haven't set up iAd you won't be able to integrate iAd into your app.