I'm afraid I got no further and looked up the answers.
I was never going to get 15a as I had the second word of 8d wrong.
For 19a, I did wonder if the English word rather than the French word for the second word was correct but have heard it said that way sometimes.
I still can't fathom 1d and 15a nor equate "series" with the four letter word in the answer.
15a is really irritating me -can't see how the NATO alphabet helps.