Thanks ProfessorM.
Did not realize that 26a will give me clashes.
Seems like wrong letters may be a foreign phrase.
I have 15 so far and they don't make sense yet.
20d is a double def 'rich' + 'supper' (in the sense of someone who drinks).
23a The notes of the musical scale immediately before doh (at the end) and the whole thing reads as the word play with the last 2 words as the def.