Hi Bastian,
I hope you are doing well. To perform goods movement in mass you can try and use the web service 'InventoryProcessingGoodsAndActivityConfirmationGoodsMovementIn'. This web service details and documentation can be accessed from the 'Service Explorer' view from 'Application and User Management' work center. More details of the web service is given below.
Name: InventoryProcessingGoodsAndActivityConfirmationGoodsMovementIn
description: Create Goods and Activity Confirmations for Goods Movements
Namspace: http://sap.com/xi/AP/LogisticsExecution/Global.
Please let me know if this suffices your requirement.
Regards,
Anand