Yes, by using a text field to add a custom URL.
Yes, that is possible.
Yes, it is possible. You can find the “max” field available in each add-on.
Yes, it is possible. You will need to copy the following tabs: yith_wapo_groups and yith_wapo_types.
Yes, the add-on contents are shown in the order and, as a consequence, in the order email as well.
No, our Product Add-Ons plugin does not work with REST API.
You can do that from the option settings and in the “Amount” field set it to “Multiplied by option string length“, as you can see in the following screenshot.
For more details about how to set up the add-on options, please, refer to this page.