16A. This is an evocative clue! [Blissful stretch] makes me think of a happy cat. The “stretch” in question is a span of time that lasts a while, if you’re lucky: It’s the HONEYMOON PERIOD.
At 23A, for example, [ Title for a tutorial on musical composition?] is KNOWING THE SCORE, a common idiom that describes someone who understands the situation, whatever it might be. The “score” in the ...