WPX6 functionality & backward compatibility

I have been using WPX3 for several years on a desktop running Windows XP Professional. I have many WPX3 documents and some older WP version files as well as several QuatroProX3 files on this machine.  This computer is getting tired and I am about to upgrade to a new desktop running Windows 7 as well as to a MS Surface Pro 2 tablet/laptop running Windows 8.1.  Will I be able to transfer, access,  read and modify my WPX3 and QuatroProX3 files on either or both of these new computers using WPX6?  Can I load my WPX3 software onto the new Windows 7 computer and upgrade to X6 or must I install the full version?  If the latter, can a get a licence to operate X6 on both of the new computers, or must I buy a separate X6 suite for each computer?