Power: It's fine for a light OC. It just depends how far you are planning to go. I'd search online to see what power draw others have reported with your CPU at various clocks & voltages. That can give you a rough idea of how much headroom you might have.
Headers: you can buy fan splitter cables which will allow you to use a single header. 3 average fans per header should be well within the power limit of the header.
It's best to have intake on one end and exhaust on the other. If you have intakes and exhausts distributed randomly then you can end up with inefficient turbulent flow and pockets of stagnant hot air.
Overclocking is pointless without improvement so your primary metric should be increased FPS in games, followed by benchmarks. Keep in mind that recent Nvidia GPUs will clock themselves up if they remain cool. GPU-Z says what is limiting a card. If it's power then you may want to raise the power limit but that will add heat.
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