well those are some pretty broad questions. to answer them:
2)if you want
4)using clay, fiberglass, wood, metal, papier mâché....... anything really. you could sculpt, mold, fold, vacuum, cut and glue,.....
What I'm trying to say is this is too broad. I'd start by looking through the forums and clicking on links people have posted. if you have more specific questions let me/us know. I'm not trying to discourage you, i'm just trying to get a better understanding on what you're after.
i mean that i need some techniques to do them, i dont even know how to sculpt the wood, but i guess im some kind of god at sculpting in clay(y really guess), about the rest o the armor, theres no problem, what worries me is the gun, i dont even have the less idea about how to make it, anyway if somebody can share some tchniques with me, thanks