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rjupiter - there are a number of library organisers that may suit you better, they target academic use more so than calibre does - Citavi, Zotero, Mendeley (it has a calibre integration plug-in), and Docear come to mind.
That said I have an economics, finance and law library of ~40,000 texts in calibre, it has less than 400 tags. I added some 'dummy books' in order to create something like a
Controlled vocabulary for tags. I used the approach as documented in
Managing subgroups of books to define the tags. This takes a lot of the arbitrariness out of assigning tag values. I do all the tagging by hand, my experience is that downloaded tags are inaccurate, inconsistent and much overloaded. If I need a new tag then it gets added to the relevant dummy book and then gets reused on the real books.
All the dummy books have Author
Z. Z. Zzzzzzz, the Titles are
Zzzz <top level genre tag>, Example,
ZZZZ Banking, is tagged with Banking.Central, Banking.Investment, Banking.Retail, Banking.Shadow etc.
I gleaned my initial tag vocabulary from LoG, WSJ, FT, Faz, Yale Law etc, took a while to set it up but now its fairly stable.
Calibre has a facility called User Categories that I've just started to get my head around (after 3 years) you can read about it in this section of the manual
Tag Browser. With the benefit of hindsight I would want to explore the possibility of using User Categories rather than my current approach.
One thing you may find confusing, I know I did at first, is that the calibre software and the documentation tend to use the words Tag and Category somewhat loosely. I overcame my confusion by mentally replacing the term 'Tag Browser' with 'Category Browser'.
Another thing I do is to use the Windows Search facility to search the content of books, this means I have to keep a searchable format, which sadly most ebook formats aren't with WDS, so I always have a PDF or DOCX version. I search the library folder directly, note I suffer no noticeable performance penalties when I add new texts to calibre. I wrote a primitive AHK script to create a CSV from the WDS results that I use as input to the Import List PI from when I create a Reading List.
If you are using Linux then you might want to take a look at this plug-in
[GUI Plugin] Recoll Full Text Search, Recoll is a context indexer/searcher for Linux.
If your using OS/X then you have the Spotlight search facility, it indexes most ebook formats. shouldn't be too hard to write an Applescript to do something like my AHK script or you could create something like the Recoll plugin.
You mentioned you're using a 7" monitor, to be honest I find it hard to imagine using calibre on such a small monitor no matter how high the resolution.
Don't give up on calibre too quickly, yes it has a steep learning curve, but it also has a level of flexibility and extensibility that is hard to match. And unlike many software products it is being continually updated with new features and improvements.
BR