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straighten, crop, adjust contrast, remove dust and crud, and sharpen
I think you have the order pretty right. Maybe put contrast before sharpen. I found G'MIC > Colors > Basic adjustments
is useful for finishing-off photos. Remember, you are only repairing with Gimp rather than creating from a blank canvas so forget the many filters and scripts.
I recently removed watermarks from a certain company in England that mass watermarks images and then tries to sell them back to the original owners. It was just time consuming because it probably can't be automated. I mainly used the clone tool for this. If you have serious problems with your photos this is the tool to use.