Hints - Not Quite A Polka

Click hints to reveal.

Hint to start puzzle: If you are new to cryptics, here is a good introduction. The first half is alphabetical, the second half is not. I wonder why answer lengths in the first half are so much longer than the second half?
Hint for extraction: These clues are downright musical! You'll want to find a suitable substring in the first half, then pair top-half answers to bottom-half answers