Because of the way it picks songs, it may pick a song that it's recently played again. But this is pretty rare.

There's definitely enough music on there, though. There are 2270 songs in the playlist. 786 of these are mine, totaling 1 day, 15 hours. I'm not sure how long the other music is, but I'm sure it's similar.
Some of the other music may be duplicated. Do you know what song you've repeated too often? I think there's a game where all the songs sound almost exactly the same, and they are all on the radio. I could maybe remove all but one of them.

Anyway, I add new music occasionally. I have some songs on my computer I plan to add, but I need to do some editing on it first.

No. It's almost entirely video game music.