Well, it's not like you *need* French or Latin to read Sayers, because I managed just fine, despite only having a slight knowledge of both.
And it's easy enough to start with the Harriet books and go back later to read the earlier books, because they're generally...not as good (but still fun). There's a pretty clear development of Sayers as a writer.
But Gaudy Night isn't even the first Harriet book, right? I do prefer to read a series in order, Anita Blake notwithstanding.
No, Strong Poison is the first one.
I always have to read a series in order. It bugs me on so many deep, completely neurotic levels if I don't.
None of it is necessary, per se. It's just more fun because Willis is making jokes and allusions to other literature.
The Harriet books, in order, are Strong Poison, Have His Carcase, Gaudy Night, and Busman's Honeymoon, and IMHO should be read in order. I'd also read Murder Must Advertise after Have His Carcase, even though Harriet isn't in it, because IIRC that's where it falls in the chronology, and it's a fun read.
I'm not a Sayers fan and won't be reading more of those, so I guess I'll just have to live with missing something of "To Say Nothing...".
Well, I couldn't get into Three Men in a Boat and still managed to love To Say Nothing of the Dog.
After reading
To say nothing of a the dog
I got
Three men and a boat
from the library, but never read it. Does that count?
Murder Must Advertise is probably my favorite of all the Wimsey books.