Worldcat as a Metadata Source

[sle7en]

Hi Hello, newbie over here!

I've just recently started using Calibre to manage my e-library and love it so far. As I dive further into it, I started to notice a few things, which raises some questions. How/Can I use Worldcat as a metadata source? Is there a plug-in out there that can pull information from Worldcat?

2 ) Also I can use some advice as a e-library starter who wants to categorize all documents by FAST subject headings. Is it a good strategy for a non-academic to start to use this system?

3 ) Are there strict tree categorization systems in Calibre? Meaning, if I don't want a file/book to be classified/tagged under 2 categories, is "text, but with a fixed set of permitted values" type of column my only option?

Thank you for all the input!