1)

I was wondering if I could replace All the 120mm fans with 24V PWM fans.

2)

I want to replace stock fans with (Noctua NF-F12 3000rpm PWM 24V or NF-F12 3000rpm PWM 12V) or will either of them would work?. I would like to replace the liquid cooling stock fan with one of these fans. 
I hope someone could answer my question.