you can add  new content  databases asociated with your web  application, but each database  only contains one site  collection data, so if you add a new content database for a new site collection, each new site data in the new site colection will be stored in the new content database.
I suppose that your WebService url  will change depending on the new site coleccion url. So if you have content in two site colecctions you are going to have two WebService urls.