(1) 'poets'is one of the four words you want - the quotation is from Burton's Anatomy of Melancholy. Enough to drive one bonkers?
(2) The twelve clues which have no definitions and only subsidiary indications lead you to solutions which are also anagrams of the surnames of poets; the apparently superfluous words in each of these clues is a quotation from the relevant poet's verse. The anagrams are real words and it is these, not the poets' names, that you enter in the grid. So (purely e.g., not from the puzzle)) 'Work at English linen, for Macavity's not there (5)' should give 'toile'as the entry, and 'Eliot' as the poet. Phew.