I had an issue with this myself a couple of months back... I have a library of over 20,000 songs collected over the last 3 years. I use to just stuff gbs and gbs into my thumbdrive and scroll like crazy with next to no flow in my music.

Now i've come up with my way of organizing (disciplining) myself. I create a few playlists (folders) for certain categories of music and limit them at about 30-60 songs. Everytime I download a song or want to add a song to my library, I will remove one that I seldom play. This keeps the folder quite up-to-date and somewhat organized. As for the rest, I still keep it in my library but in an external hard disk outside my laptop harddisk to save space. Chances are, we'll never listen to them again, but again I'm a collector of songs haha.

Probably in your case you could make a smaller playlist for each category if you're just using for your listening pleasures

Definitely use playlists to organize your stuff, and keep multiple backups of all your music in different locations (hard drive, cloud, pc, phone, ipod, etc). Your drives *will* fail one day; it's best to get in the habit of regularly backing up your music.

Hard drive space is cheap these days. Just buy a 1TB and you'll be set for a very long time. In fact, buy 2 hard drives. Keep one at home as your 'if everything else dies' backup, and use the other one as your main music collection. Back it up every month or sooner.

To keep up with fresh music, the only way I know is to listen to music all the time. Follow your favorite artists, labels, sites, channels on SoundCloud, Youtube, Mixcloud, and so on. Set aside plenty of time to troll through your streams and pick out music that you like. Doing this sets you above the other DJs who just do the Beatport top 100. There's no shortcut to diggin'!