I have a 64GB drive in mine, with only about 3500 songs. It is only there as a backup to the backup that is on my phone, which I only use if there is no cell service to reach my Amazon on-line music. I will say that is is glacially slow at finding folders and songs, the interface is terrible. If you try scrolling a bunch of folders, at some point it hits a limit and won't respond until a time limit (presumably to force you to pay attention to driving). What I ended up doing is first something like you did, folder paths of root > artist > album. But I don't like fussing around with finding an album to listen to (and it's just too slow), so I also have a folder "AllMusic" off the root, that has a copy of the same music all in one big folder. Being near the top folder (alphabetically), it's easy to find, then I just hit the Shuffle button and off it goes to randomly play tunes.
If I do nothing, it drills into the very top folder (10,000 Maniacs), very top album (Blind Man's Zoo), then it starts to play the first song (Eat For Two). Every single time.
I will say that having music on a USB drive delivers the highest quality sound, as long as you burned them using the highest sampling rate. It's too bad the interface is so awful.