42, The answer is always 42........
No seriously, everyone else answered your question so I won't repeat them
Let me give you some guidelines with Gears Of War:
From what I can remember, the main characters were around 12 to 15k
Guns: 3 to 6k
Buildings: Put together in sections, so really no way to tell.
That probably doesn't help you at all, but it's the best I have