You do not need to install all those updates.
QuarkXPress 7.5 did have a complete installer. I do not see the links on the website. However you can get in touch with the FREE Chat Support, they should be able to help you with the link.
Once you have the latest installer, you may install with respective serial number on QuarkXPress 6 (You can install QuarkXPress 7 even if the machine does not have QuarkXPress 6, all you need is the original and the new serial number).
[Edit]
I got the links for you:
QuarkXPress 7.5 Installer Mac:
http://files.quark.com/download/QXP/qxp4603_installermac.dmg
QuarkXPress 7.5 Installer Win:
http://files.quark.com/download/QXP/qxp4603_installerwin.zip