I’m tracking these requirements too (for my upcoming album, which will be available online). It’s similar to your list, but because it’s an album-website and not only song-entries on a blog, there’s also cross-linking between related songs.

A generic model of these cross-linking requirements–some of which might be applicable to blogging, could include: links to playlists that include this song; previous song / next song tracking; and a general sense of sequence (e.g., play all Lucas’ songs from July, order by date).

Also, what you have as “annotations” could be split into some categories, like credits, lyrics, recording date, recording location, instruments used, etc. Credits might include other musicians, producers, composers, etc.

Also, you might think about “annotations” in terms of something like the Wikipedia entry on Purple Haze, e.g., both in terms of the way it has an internal structure of “types” of information / data, and also in terms of it’s design as a hypertext document with cross-linking.

(Of course, I know: your blogging, not wiki-ing. . .)

For example, I haven’t quite understood how you’re choosing songs. And, I could imagine each song referencing “indexes” that provide both more context for how your collecting songs together, and also cross-referencing between the songs and their sources (be they sources of the sheet music, composer names, original instruments, year, country of origin, etc.).