Where to start ?
5A - in which Caldwell takes all ? (7) I have ??????T
12A - sounds like single heretical principle defended by Priestley (9) I have ??V?????N
17A Dressing from Titania's fairy seed (7,7) I have M???A??, ?N?S?E?
26A - Orsino implied that he would find it musically acceptable (7) I guess this must be surfeit buyt can't make it fit with 25D which I see as 'spy'