Ditto. I did the same for my partner for his Lego instruction booklet collection. He have over 150 sets and managing all of his Lego booklet (through Lego official app) and the official Lego website don't have every single booklet. And those PDFs are rather large file (averaging 40+MB, some are 100MB, a few is 200MB). It wasn't feasible to keep it all in his iPad due to the storage space. So I used my desktop to handles that for him. The best thing about calibre-web, it allows him to upload the PDF and edit the metadata directly in his iPad's Safari than depending on me to put it up for him (I don't mind doing for him, just that I have terrible time management.) For him, he don't have to do manual management and it is in one place.
Right now, I am trying to set up a scrapping the metadata from few sites in calibre (Import List plugin). Because LibraryThing, WorldCatalog and Amazon are usually scrapping for books. The thing is I don't know how to do XPath expression even I tried to read the guide. I couldn't understand how the hell it work. I can understand LaTeX, Homebrew, Chocolatey, Bash, CSS documentation just fine, but XPath I am just dumbfounded.