Mortherboard standoff question

[SM Phoo]

So I wanna build my PC, but not happy with the layout of the P5 so I'm gonna drill some holes so I can attach my mobo.

Looking on amazon for some longer / higher stand offs, I've come across brass and nylon. I did some googling to see if their is any difference, and people spoke about using washers, using brass etc, to avoid shorting the mobo, but at the same time, that seems like an old problem, for older boards, so my question is, does it actually matter which I use, and would brass be a stronger material to use?

 

Two side questions.

I did ask this once before, but most cases have a big gap where the mobo sits, just behind the CPU, is that purely for ease of access, or does it serve any other purpose

I'm thinking of using a carbon fibre wrap on the case, this is probably a stupid question, but it wont cause any problem with shorting I assume?

 

As for shorting, I assume it only matters, metal on metal?

Thanks