Large audio collection - need help with setup

I hear you.

My music collection is just under 10,000 songs and 91gb (slightly less if I properly de-dupped it).

I was thinking of coding some software that could manage it all.
I've created SQL Server databases will millions of records in it before, and with dedicated hardware it's fast; under 10 seconds for a full scan of millions.
30,000 rows in a table is nothing to SQL Server.
and loading up a saved playlist would be instant.

There are a lot of nice players out there, just need something to manage the collection, search and compose a playlist to pass on to the player to play.

Eventually I might be forced to build something out of sheer necessity, thus far I've gotten by by sorting my music into artist operating-system folders, and correctly named files; and managing small playlists in foobar manually.
Metadata is another ball of wax. Correcting it isn't something that interests me from a coding perspective.
I'm not a pretty-pictures type of person, I'm not interested in looking at album covers and/or album names. Bare metal filename is good-enough for me to know what it is. (Maybe I've just lived too many decades without that stuff... LOL)

But when I read things like "the software slowed at just 5,000 or 50,000 songs" it makes me sigh and cringe at the programmers who make such drivel... the boss probably hired some know-nothing, someone fresh out of school to make it.
Files and File Info shouldn't be used as a replacement for rows in a db. (good god! pulls hair out!)

I have similar requirements to you (except I have an iPod Classic 160Gb, which will keep me for another few months), I have about 20K songs, mostly ripped to ALAC, although a bunch are in MP3/AAC since I purchased them from iTunes/Amazon. Mostly I purchase CD's and rip to ALAC using dbPoweramp. Collection size is around 400Gb, stored on a Synology DS213j.

1) Ripping and initial tagging is handled by dbPoweramp.

This works fairly well, although the metadata available from open sources is sometimes screwed up. Cover art is generally available in 800x800 or so sizes and is embedded in the file.

2) Import into iTunes using the Import directory function of iTunes. This leaves an an extra copy of the CD on the disk, I put it in an area which is not indexed by my music server.

3) I use an auto-tagging program called TuneUp to clean up the tagging from dbPoweramp. This works very well for most types of music, classical is problematic since there is no agreed upon standard for tagging artist/orchestra/composer, etc. Compilation albums, especially career retrospectives can be prolematic also, although not nearly as bad as classical. However: it does a very good job of tagging just about everything else, even if the existing tags are null or incorrect. This will make it reasonably easy to get your collection tagged in a consistent way.

For playing music I use one of two DLNA servers. For my living room, I use the Synology DLNA server and the CP/Renderer in my Denon AVR X3000. This plays ALAC natively so no transcoding is necessary. In my bedroom I use the CP/Renderer in my Dish Joey which does not handle ALAC. For that I use Minimserver and have it transcode ALAC to WAV.

Sometimes I use BubbleUPnP on my Android phone to create playlists on the fly and have it control the renderer in the Denon. Much more often I use the Denon software directly. One thing I do like about the Synology server as opposed to MinimServer is that the Synology keeps the last 27 or so times you have added content easily available through the "Recently Added" section. Since I am always adding stuff, this makes it easy to listen to my newest acquisitions.

You'll have to come up with your own system for managing the content on your phone. Like I said, I keep my whole collection on my iPod Classic. When that gets too small, I'll turn in into a Frankenpod using the gizmos from:

http://www.tarkan.info/

He has a way to made a 1Tb iPod using an SSD!