0pt0 - some hints. Hope this isn't saying too much - but, as the puzzle is so difficult, I hope it's OK.
20a - Where would you find the first word? How might the third word be described?
3d - definition is last word. A proper name about 'E'
4d - definition is last word, take the top off a word meaning the rest of the clue...
18d - definition first word, wordplay 4 inside 4.
21d - the definition is the whole clue, wordplay letter by letter
22d - definition first word, 'sounds like' wordplay.