Hi,
1. If the Joomla content plugin or module you're using supports Vimeo, you can embed videos from Vimeo yes.
You can use any module and most of the Joomla content plugins. As an example, I've personnally used OSYoutube with youtube videos and it worked just fine:
extensions.joomla.org/extension/osyoutube
2. Then create a characteristic with two values "with customization" and "without customization", add the characteristic to the product. Then, edit the "without customization" variant via the Variants tab of the product and in the "Files and images" area, add the file. That way, the file will only be provided to the customer after the purchase if he selects "without customization".
You'll see the variant selection everywhere: in the order details, in the invoice, in the email notifications.