This sounds interesting! Have you watched Twelve Monkeys and Gattaca? They could give you some ideas, as well.
It would definitely be a plot-heavy kind of game and something you would have to seek players from outside the world of places like pbads or rps. It would be ideal to already have a handful of trusted players who had the time to dedicate to a game like this, to make sure that it would make past the usual unsteady first few weeks.
As a moderator, I think it would be wise to have a couple of months of pre-determined plot and work around that with the characters you do have. Maybe not full-out premades, but describing a few main roles or even describing the characters free for the taking by their tasks would be interesting. Also, the connections between the main characters would be a great help in getting interaction taking place.
I would say if you go for this, keep the community small, around 15 characters, so that the plot can actually be developed. I would also say, if possible, not to make it a journal based game. In the sense that interaction should happen in third-person and, first person only through correspondence such as e-mails, phone calls or text messages. Unless, I am reading it wrong, but I don't think these agents would be commenting back and forth on journals and that would take away from the realism of the entire thing. I say definitely keep it focused on one group, before widening the reach of the character types. But, a very good idea overall, if you have the time to stick close to plot and making sure players are around and interested in following through! Definitely hand-pick the players for the roles.