[Andrew Stephens]

I need to write an automated script/action that will open several thousand photoshop files, convert them the cmyk, resize them and set them to 300dpiu before saving them as tiffs.

Best to write a batch action in Photoshop or use automator?

[Veltliner]

Why not create a simple Action, then mark a certain number of files in image processor, and run the action.

You don't have to run all those 1000s of files at once.