Flickr2Commons is a tool written by Magnus Manske to easily upload single and multiple files from Flickr to Commons. This tool uses OAuth to upload files to Commons. When you get to the tool's page, make sure you authorize first!
Instead of carrying a very large number of photos from a unique Flickr user ID or name, you can upload them by albums (using the Flickr photoset ID). It may bring a little bit more of work, but you will be able to easily and proper customize description, categories and avoid later corrective editions.
Watch out for the auto-tags and auto-detect categories; it may add undesirable additional categories to the photos.
It is important that you upload photos with an understandable title, preferably in English, thus preventing file names with automatic prefixes such as "DSC_" or "IMG_". Names containing "double spaces" and symbols like "@" are also a problem when you try to upload files to Commons. To handle with all that, you may use, for example, addons such as Find and Replace, for Firefox.