Well, here I am again. I believe I've solved this one except for 4D, "Did this doctor's companion have any sex-appeal? Maybe" I have N?S?A and am stumped. Assuming the second letter must be a vowel, I tried plugging in each one (including "Y"), and running through possibilities for the fourth letter. Nothing rings a bell! Either it's really obscure, or I'm being really dumb....
Thank you so much! No wonder it eluded me; I'm not that familiar with Dr. Who, and I also misconstrued the clue (was looking for the name of a doctor with a companion, not the name of the companion of a doctor). Cheers!