I've been staring a this one without much progress. Can someone please give me a general hint as to how to proceed as well specifically the answer to 16a One very leggy girl weed picked up (9) MIL??????
It's to do with maths - three of the unclued answers contain numbers (one of these crosses with the thematically treated entry of a straight clue). The puzzle number is significant.
Yes, that's how the wordplay works (but 'mille' sounds the same as 'milli').
It's definitely an 'E' in this instance bacuse it's a checked letter in the crossword.