How do I use robocopy with a large number of excluded files?

There is a limit on command line length (I think it is something like 2048 characters) in windows.

You should generate a job file with a small subset of the exclusion list specified (using the /save:filename argument) to get the syntax, edit the file to include the full list, and then use the /job:filename argument to run it.

For reference, the documentation for this tool can be found here.