I use a few constantly, but, the ones I think could be automated, already are.
The plugins I use a lot are: Kobo Utilities (anyone surprised at that?), Reading List, FanFictionDownloader, Count Pages, Annotations, Smart Eject. I will also use ePubSplit when needed and Open With when I want to look at an epub in Sigil instead of the calibre editor. I'll admit to having most of the plugins installed, but rarely use any of the others. And there are a couple of others written just for me.
FFDL already has some automation. I have it adding books to Reading Lists and starting Count Books. It can also use Generate Cover, but I don't have that configured. Apart from these, I can't think of anything else that would be useful.
You might also want to consider when to start the automation. Both Reading List and Kobo Utilities have functions that are triggered when a device is plugged in. There are a couple of other plugins that might benefit from that.
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