case fan help?

[HiDood]

I have a spare deepcool fan and is there a led cable that can be plugged to the led switch from the case? I mean it's not necessary but let's not waste it... Right?
Second, should I go for positive or negative pressure? I have a 120mm fan for exhaust and 1 120mm noctua fan and 1 120mm deepcool fan. How to place these fans and connect them to the led switch? I could also go for a 140mm fan too! Oh and the one and only chassis fan slot is full.
Lastly how to distinguish fan directions? Yeah it is a noob question.
The case is a cm storm scout 2.

 

[Ithaca]

Is there room for an intake fan on the bottom front position? There usually is, and this helps airflow significantly. You normally want air to be taken in at the bottom front end and flow through the case upwards towards your rear exhaust fan. Side fans should usually be mounted as intake, as they could otherwise disrupt the airflow from front to back of the case (and possible draw cool air away from CPU / GPU components, which is bad).

I'll rule out the PSU from the equation, as it should draw air from below the case and expel it through the back without affecting the rest of the case (on this chassis the PSU is mounted in the bottom position).

I would set your case up like this:
Back: Exhaust fan (most efficient cooler goes here)
Front: Intake
Side: Intake

Do you have fan grills on the top of the case? In that case:
Top: Exhaust fan

Also, the type of CPU and GPU coolers that you're using also have impact on the airflow of the case. What parts are in there?

In general, positive pressure is known to prevent dust accumulation, but negative pressure is known to give slightly better temperatures inside the case. Both have their benefits and I will leave that choice up to you.