Sorry to add to the confusion with the potter, we have since found the "equipment" under her little sister's bed.
I got back from a walk and seemed to suddenly be able to fill a lot it in, but still can't get 4d or 16a despite having all the crossers. I can't see any hints for those already but apologies if I've missed something.
Not really enjoyed this, but need to finish it now 2 left.
I think 11a is my COD.