Hi, Rusty!
Ah, thank you very much!
Yes, I can see how you have arrived at those answers ...but I would have never got there at all, without your very kind help!
(I should have invoked the proverbial cows again......)
There is a New Zealand crime writer called Ngaio Marsh.
"Toponym" is a new word to me.
Now...25a: Chips Peter had with spoon at wedding (6)
This is how I have parsed it.....
"quince" - double definition
Peter Quince is a carpenter / "chips" in "A MidSummer Night's Dream" (secondary plot within)
"Quince" is also what "The Owl and the Pussycat" ate with a runcible spoon at their wedding, in the poem by Edward Lear.
29a: Thus Vincent’s night visit, entertaining bishop (6)
"starry" = "thus Vincent's night" (def)
stay - visit
RR - Right Reverend (bishop)
"Starry Night" is one of Vincent Van Gogh's paintings.
I hope these make sense to you?