Yes, indeed, fixing metadata manually can be a chore. The ideal is to get it right when you are ripping the disc and avoid having to fix the data afterwards.
I use DBPoweramp for ripping. And I can attest that none of the free databases in DBP (including Freedb, etc.) will give you the consistency that you need for classical music. DBPoweamp allows you to override the suggested metadata before ripping and that is when I make corrections. I have my own workflow that I use for consistency. That helps solve the problem of Artist vs Album Artist and also the inconsistencies in the names of the composers.
I use MP3TAG to automatically change name of the track file and fix an occasional item that I decide to modify after ripping. (For classical, I like to include composer, performer, composition, track name in the name of the file. For example: Mahler-Solti-Symphony No. 5 - Part III Adaguietto. Mp3Tag can do that automatically in batches).
Several folks here have recommended a software package called MusiCHI for metadata. I am not familiar with it but have read that it is very thorough. It is recommended for classical and jazz. It is not free.
http://www.thewelltemperedcomputer.com/SW/Players/MusiCHI.htm
Your fear about losing your data when using Roon is unfounded. Roon will read your files/folders and internally catalogs your library. But it does NOT change or alter the location or structure of your folders or the data. Your data will remain intact.
In fact, you can tell Roon if you want to use your current metadata or if you prefer to have Roon to use its own. Your call.
Before spending any money on hardware, you should try Roon for free. You can install Roon core in an existing computer and have it point to your different drives (NAS and USB drives) to find your music.
Your sizable library will benefit greatly from a powerful music data management like Roon. Not to mention the sound.
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