Google adsense using rule to serve there adsense publisher Via "publisher ID "so careless the amount of the website as long the website using your publisher ID it serve as your adsense code for comission
No. You can submit a best site and apply for adsense. Then u will get approved. Then u can put adsense in your other sites also. But dont put adsense in adult sites and dont violate andy google adsense TOS.
No, once you'll get your first visitor ( assuming that you've just created a new site ), they will receive a ping and it'll be automatically added to your account ( however, you will not see it anywhere ).
I said that when you place your add on a new website, google receives a ping and it's automatically added to your account ( so you should not go to your control panel and add it manually ). Still didn't get it ?