If you get an delete request from a user, you need to handle the following items.
You need to use Joomla! user management tools to delete users.
The overview page of Event Gallery in the backend contains a link which allows you to delete carts which are older than 30 days.
You can delete orders from the order list in the backend.
There are different log files stored in the log folder of your Joomla! server. You need to clean them manually if needed.