I need help from an extern however I don't want him to have access to the customers data. Thats why I want to delete it and after he is done, I want to load the backup. How should I do it?
To extract orders you can use the following extension https://www.magentocommerce.com/magento-connect/bulk-import-export-orders-to-csv-1.html
Here is the paid extension to extract/import order data https://www.aitoc.com/en/magentomods_orders_export_and_import.html
Extension to import/export customers https://www.magentocommerce.com/magento-connect/bulk-advanced-customer-import-export.html
But it may not be the best way to go, I would simply create another user account in magento and disallow Customer and Order data to be viewed on his behalf. Such solution only works when they don't require access to Database. Here is the explanation: https://www.simplehelix.com/blog/magento/14930/