I think the key to casting the DP staff is to pick people who can bring some real personality/character to the roles and not come across flat or boring (most of the characters in SR came across this way to me except for James marsden). These people might not get the most screen time in the first film but you should still feel something for them and want to see more of them.
A character like Ron Troupe might not be the morst interesting, but casting someone like Mos Def to play him would immediately make the character more appealing/interesting, he could give him a much more distinct personality. And he could add some nice wit/humor to the DP.
Also with Cat Grant, you not only need someone who's attractive but who's got a good strong personality. natasha hendridge i think would bring in both those aspects of teh character and since she's a little older now, you could play with how she's characterized in teh comic now, she's a gossip columnist who's kind of a cougar. While Natsha isn't old enough to be a cougar you could characterize her as someone a little past her physical prime but still thinks she's hot stuff (and she is still quite attractive). You could also play with her former characterization from the 90s as a potential love interests for clark aside from lois. Not that clark is interested but that she's a little into clark or at least flirts with him.
I really like the idea of making the DP feel alive, vibrant with life. I also think people who've done both serious roles and some comedic stuff would be the best to cast as seeing these characters interact could be fun and a little quirky if handled right.
Also i went for John Mahoney b/c he's also done both comedy and more serious roles. He could bring that to the role of Perry quite well i think.
