Ukridge, I have many, many fewer than 80% of the answers but I do have 4d (I think). Definition is first word and is arguably slightly obscure depending on your knowledge, but the wordplay is quite straightforward parsing, including a reversal.
I have neither 3 nor 5 of the downs sadly! Thinking 5d might be defined by the last word, and the wordplay is close but I can't quite get it to match up precisely so I may be on the wrong track...