From the viewpoint of a long-time goldsource player - I can imagine this becoming interesting. Although, the biggest problem is making expansive outdoor maps as indicated in your routes. But I have a few gripes, not general ones like huntey is discussing, but details on each page that I feel should be elucidated.
Page 1...the red character will be around southwestern Australia, pass through the Indian Ocean, take place around Madagascar, head towards Africa, turn back, and end up in Africa.
Wait, what? He goes towards Africa, turn back and end up in Africa? So he doesn't escape Africa does he? Good ending.
Boarding boats is prolly do-able via a boat chase scene or something. I've seen plenty of chase scenes on trains but not on boats before. However I doubt that anyone is willing to make a boat-chase map that's even half as impressive as the one scene from the dream compo winning entry. A shame.
Implementing the second mode is easily doable: One is the "new game" and the other is the "training". This has been done in residual point, it's cool.
Since they overlap in africa, it is highly favourable to have one or a few maps that are accessed by both the american and the soviet 'marine'. Sorry, I just never seen the words 'soviet marine' used together like that. Looked weird.
Although most of the game looks as if it will be almost completely overseas, there will be areas where the player will rest to see he had advanced for a long amount of time. There could have been certain twists or disasters that the player missed which could be kept a mystery for an amount of time.
This part is too vague. I'm assuming you meant cutscene-game_text combo that furthers storyline. Completely do-able.
I am also confused on why the soviet marines (lol) come from Australia. I'm sure the admin team is going to love this idea.
Page 2 - The NPC list.
1. A typical american marine. surely the hgrunts can do for these guys. I have models of the hgrunts using CS ak-47's and m3 pump shotguns from fpsbanana so no worries.
2. Soviet marines (lol, sorry) - just skin them red with soviet emblems on their shirts. Although, the sledgehammer is a problem. I know a mod that has sledgehammers but there aren't w_models.
3. Boat mechanic - easy. Port the TFC engineer and give him the tfc wrench. Probably act similar to barneys. (except the weapon)
4. Generic wild monster. Easy, any monster using the zombie code will do melee attacks.
5. Generic critter, much like monster_rat. No problem
6. Generic flying critter. Can use flyer flock code for flying, but has a hitbox so it can be killed.
7. Kenyan - well if they are easily startled I guess you mean them to be scientist-like.
8. Beast that triggers your geiger counter - kills player with one bite - this is bad for game play. Never, ever use NPC's that kill in 1 hit. The male assassin with sniper from op4 is supposed to kill in 1 hit, but they only do a measly 15 damage. It's purely for gameplay reasons.
9. Helicopter with nuke. I don't understand how HELICOPTERS can lug a nuke onboard. That will raise eyebrows.
Page 3 - storyline - 7 comprehensible chapters... PER character
that makes 14 chapters total... that's almost nearing the number of chapters in the vanilla Half life. That's a bit overly ambitious. People may not have the effort or the dedication to map for 14 chapters.
Soviet marine chapters (lol, sorry couldn't resist)
1. What was the message? Well anyway a typical intro with early fight (people might not yet be adjusted to the game to be already thrown into a fight)
2. Gets weapon, but no fighting, get knocked out, end up on the island. Ok I guess he can explore the island a bit before he finds the radio tower (placed there by mysterious stranger TM)
3. More menial tasks (possibly puzzles) on ship. Player does not find the horror.
4. Rest on land, ship blows over. Boss battle. Okay.
5. Occurs entirely on high seas. The way I see it, it will be hard to do unless done as a cutscene. And then a helicopter boss battle.
6. Player goes thru African jungles (very hard to map, massive amount of props required), fights some enemy soldiers, and then some bogies. Player is told to escape, not fight. Sounds a wee bit like Predator (the film).
7. The player is killed, after all that trouble.
US marine chapters
1. Chopper ride to africa. Most likely similar to the one in Heart of Evil. Then a boat ride. From North Africa, around the cape and over to madagascar. May take well over 20 maps of boat rides (jk, just compress it into one cutscene)
2. It just occurred to me, why did the US marines take the Atlantic ocean route to madagascar, not the pacific ocean route? Also in the map it looks like they landed near west africa and just took the overland route? I'm confused.
3. Boss battle on the high seas. On the ship.
4. This is most certainly where the overlap maps may occur, if any. A gruntfest chapter.
5. Player gets weapons stripped? after being knocked out, in similar fashion to soviet chapter 2
6. More bosses.
7. You kill the other character you played (the soviet character) cutscenes with text flash up and tell you that you were killed maybe 20 years later right after you retired. Nobody wins.
Final Page - weapons
1. SOVIET WEAPONS
weapon_fists - seen this in plenty of mods. Probably a crowbar replacement with different sounds.
weapon_pistol - replacement for glock. Prolly a stenchkin aps or tokarev.
weapon_mp5 - replacement for the, um, the mp5.
weapon_shotgun - replacement for the gluon gun. Nah just messin' with ya. I mean the shotgun.
weapon_wrench - for consistency, probably from tfc, or op4
weapon_rpg - do I really have to tell you any more
weapon_sledgehammer - Like I said before I've seen this in another mod but in this case op4 pipewrench code will prolly work.
AMERICAN WEAPONS
weapon_fists - same deal.
weapon_mp5 - same deal.
weapon_sledgehammer - dunno american marines had experience using sledgehammers in combat.
weapon_spear - dunno. The only spear I've seen is in Afraid of monsters Director's cut. Not easy to implement. (unless if it's yet another useless crowbar replacement)
weapon_shotgun - not a different deal.
weapon_rpg - not really a different deal.
weapon_chaingun - the peak of American identity. Blasting away with a chaingun. Although TF2 players will agree if this weapon were to be given to the soviets.
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SUMMARY
There isn't much in terms of coding... but the maps are a bit vague and, frankly, too much. No one on TWHL (or anywhere, I venture) will dedicate to make 14 chapters worth of maps for a mod like this. However I will tell you how this mod is possible. Once you have made (or have someone else make) the 14-chapters worth of maps, show some aspiring screenshots of said maps, then put it on moddb, rest assured coders will appear sooner or later. As it is now I doubt it will be able to climb out of the cradle. Sorry.
*And it IS possible. People your age have made full mods (Afraid of monsters for instance)