Wow. This really, really, really sounds good to me! Some (not so) minor thoughts :
I realise you're only in the storyboard stage yet, but you should seriously start to consider the limitations and potential of the OFP engine. A campaign would be quite profitable, I believe, for a number of reasons:
Eye candy. I cannot stress this enough. Ever played Conspiracies? I never played past the first bunch of...err...area-things, admittedly. Mostly since I'm not that good at German and I apparently missed some large slice of storyline, and I wasn't much for OFP-approximation of zombies. BUT : the surroundings were simply amazingly beautiful. Of course, I'm not saying you should invest quite that much (=hundred of mb's of addons) into eye candy, but by making smaller missions you can add more placeables and units and such without risking too much lag.
Eye candy is vital, together with good voice acting and camera scripting (a.k.a. Abandoned Armies) to keep interest in the plot, when there's no shooting going on. Remember that while the player isn't engaging the enemy, blowing up stuff or playing soldier, you're basically scripting a movie. OFP isn't made for a relationship drama or love story or 2001 Space Odyssey. It IS made for war movie, spook thriller and action however. Which means that whenever there isn't explosions or special effects or cool gadgets being showed on screen, you have to have some pretty hard-boiled dialogue, good atmosphere and fascinating plot to keep the "viewer" interested.
Also, the original plot you outlined (going from a few overt actions with a lot of sneaking about undetected, into full-scale SEAL behind-the-lines sabotaging work) sounds like it could have elements in it for everyone. The question is where you want to put the focus : on the initial sneaking-about, or the later more "common" OFP-gameplay elements.
I suggest you build up a strong storyline. Add a lot of characters; resistance members, agents, double-agents, adverseries, allies. Develop the original trio's character as well, make each an individual, so keeping them alive isn't just a matter of gameplay, but something the player actually WANTS. Ergo, make 'em more than just that stupid AI bastard running around 5 meters behind you. Do this through the initial phase, make sure to add as many dynamic elements as you can : what you say or do or how well you do it determines factors in later stages of the campaign. I.e. you let a resistance leader die instead of compromising your cover, and later it's revealed that man could have given you vital info on an enemy encampment you're supposed to scout out, as SEAL operatives.
Basically, you could combine the two parts of the mission into a harmonic whole that all cadres of OFP players could enjoy. The initial "roleplaying" or "adventure" styled missions could be passed the easy and fast way, with a minimum of extracurricular activity. For instance, HQ could leave it up to your judgement of the current situation if wether or not you should try to infiltrate the town by night and attend the secret underground gathering you've heard of (thus maybe gaining valuable information/aquaintances, against the risk of getting caught by town police/Russian patrols), or head off into the night and gather the intel yourself.
Wouldn't it be great if you'd find that your actions could change the entire course, or ending, of the campaign? That that one captured and tortured professor emeritus of Lipany University you rescued was elected president when everything was over? Or that because you were compromised too early that one time, everything escalated into nuclear warfare, the last Nogovan Times ever printed having the words "US NAVY SEALS identified as the saboteurs!". Or any number of alternate endings.
Yes, I know. WAAAY too much work. But I've always been one to think that you should aim high rather than low. As long as you can reach at least a couple of your goals, you've probably gone further than most.
And hey : Armed Assault is still some ways off. And besides, scripts, recorded voices, general storyline, dialogue, character concepts etc are easy enough to port over to Arma.
So don't despair.
I'll be following this project with interest.
/Wolfrug out.