How many missiles or grenades do you get for the req cost? I thought I saw it listed somewhere but now I can't find a specific answer.

It's very specific on the grenades with N/A that you will only get one when they decide they might be required, but I assume that's a special case and the fact that they say you only get one implies you get more with the others.

Grenades: I'm not entirely sure. The only time it's really come up for me, I used the Tac Marine standard issue as a guideline.

Missiles: As per the rules on weapons for ammo. Functionally infinite standard ammo unless there's some reason to limit it. If there is, I believe that the number becomes 2 spare reloads.

and when you req special grenades or missiles?

As I said, I kinda winged it with the grenades. As to special missiles, it would be as any other special ammo, and have req cost per "magazine"

i don`t know? how many do you think your space marine can carry with thim with out turning him into a walking municion crate?

if you take in account rule of 3 then any where between 3 too 18. missiles in DW always lookt too me as a weapon you only care with you when your sure your going too need it a well used heavy bolter can do wat more damage IMHO