We do quite a bit of uploading of our British Library digitised collections to Wikimedia Commons and using their GLAMwiki Toolset allows us to fashion our metadata up front so it is consistent, and upload files in bulk by collection. This bulk uploader utility requires metadata to be in a flat-XML file.
There is actually quite a comprehensive guide over at Wikimedia Commons on how to get started using this tool but I thought I might also share an example of how we do it over here! In particular, how we use Open Refine to quickly turn a spreadsheet of records into an XML file appropriate for use in the GLAMwiki Toolset from a spreadsheet of records.
http://britishlibrary.typepad.co.uk/digital-scholarship/2015/12/using-open-refine-to-create-xml-records-for-wikimedia-batch-upload-tool.html