I have a large CD collection and decided to re-rip the entire collection to a high quality format. After experimenting, I settled back on the mp3 format because it works on every device and the quality is good enough for every audio player I own.
My encoder is Exact Audio Copy (EAC), which is free. I chose it because it does error correction, and some of my older CD's are pretty scratched up. For quality, I set EAC to rip the audio tracks to WAV files, and then reencode that lossless file to 320kbps (constant) mp3, which is the best quality available for that format. EAC can be set to automatically delete the WAV files after compression.
EAC is good about finding the meta data for the audio tracks, and can organize your folder and file name structure in just about any way you choose. Because my Plex music library is fresly ripped, and all of the files contain complete meta data, I organized my files into folders by artist with a sub-folder for each album title. The files are named by the song number and song title. Plex has had no trouble identifying and presenting my files correctly, and I recommend taking the time to rip fresh copies of all the music you want in your Plex library.
Plex seems to group artists by the 'album artist' field in the mp3 tag. If, for instance, you have records from 'Miles Davis' as well as 'The Miles Davis Quintet' and you would like them to all appear under 'Miles Davis' in Plex, just be sure to edit your mp3 meta information accordingly.
When you add music to your library, Plex will automatically find and download the album art, some basic band bio information, similar artist information, and even information on upcoming concerts for current bands. You can manually update the album art and background photo for artist and album pages, as I have done in the screenshots below.
Plex automatically downloads artwork for the artist, and for album covers. But you can drop your own image files into the folders and Plex will default to them.
An image called 'artist.jpg' inside the artist folder will cause Plex will default to that image.
An image called 'background.jpg' inside the artist folder will cause Plex to use that image as the default background for every page under that artist.
An image named 'cover.jpg' inside an album folder will cause Plex to use that image as the default album art.