i love the idea. it's a huge project tho. I'd help but I'm not that skilled in anything :P.
However i can help out with the story and stuff. now, about the idea for you being a clone of Gordon, I don't think that would work. RPG's are meant to be played by a lot of people at once, it just seems stupid if there's like 50 clones of Gordon running around the place at once.
It would be much better if each player is a different individual. The player doesn't necessarily need a back story. it's up to them what they do with their character. If all of them would be clones of Gordon Freeman, the feeling of individuality would be lost. also, it would make no sense if you were able to customize your character... since hes Gordon Freeman, one individual man.