i think a moderator should be one not relevant to any particular sub forum. if a moderator needs to move a thread or delete spam, then that should be across the board. likewise if a thread needs to be closed. i'm not sure that moderators need to delete accounts - spammers or trolls. it depends on the work load that administrators have to deal with. i can imagine that approving images takes a certain amount.
but admin will also be able to appoint new moderators should they be needed. keep in mind some mods will be away from the site for different reasons. e.g. i was gone for the last month to try and concentrate on photography. i was also doing a little work (3d ).
having said all that i know that
is more upload orientated than discussion orientated, so the forum will probably take a second place over all.