In regards to the GDPR, you can allow your users to download all their data from the profile page / widget on the front-end of your site.
You can track the clicks in your emails with AcyMailing, and/or Google analytics.
You can also choose if AcyMailing should also collect data on clicks for links not leading to your own website or only internal ones.
Example of an external link: https://www.google.com