Problem with having too many fans, you end up having a less efficient airflow.
You'd prolly have to mess around with it to figure out what would be best, especially for the CPU HS design. Tower HS usually would want front to rear.
Basically you want more negative pressure then positive, thus trying to pull out heat rather push it out. That would be more of a traditional setup. I do have a CM 590 case to where I use the top exaust as an intake, since I use a Tuniq Tower HS. I have it setup to a Fan Controller (5v/12v switch) to where I will turn it on when it does get hot from the cores being under load, to push cool air infront of the HS. So that would be an example that would depend on the HS.
Yes, Led fans would eat more power then fans without... it would be about 1w at the most.