I have been creating mood boards also on Pinterest to map my ideas. I feel because it is in black and white it needs to be made interesting. By adding texture to the portraits it makes them more individual.
For ideas I have also look at the other magazines suggested in the breif such as ID, Monocle & Harpers Bazaar on their websites to get an idea of the looks that they are going for:
Which has given me a good idea of what the photographs should look like.