Costruire un Negozio Online

This is the link of ecommerce -> [login to view URL] I need a customization in the checkout page: - if the country is selected to "Italy" must appear two fields: "Codice Fiscale" and "Partita Iva", required one of this two....for example, if I write in to Codice Fiscale field -> Partita Iva is not required, or if i write in to Partita Iva field -> Codice Fiscale isn't required. Both fields validate by alphanumeric. - if the country select is one of the country of the Union European ([login to view URL]), Italy excluded, we need a custom field called "VAT" but is not required. - if the country select is a country that is outside of UE and the Italy, we don't require any custom field The fields must be inside the template called "minimalism" and extension "onepagecheckout", moreover the fields must appear in all documents: mail order, invoice, etc....