I'd advise against building your own SMPS if you don't have much electronics experience. The component choices and design of the actual power supply isn't trivial. As you'll need a very high current supply the chances of it going kaboom with spectacular results are high. Patrick probably knows a lot more about this.

What I've done is to replace each individual linear power supply with a SMPS replacement. It's reduced the amount of clutter and they don't hum like the old ones did. I did briefly consider using a large prebuilt SMPS to power the lot but it would require a fan to cool. All of the ones I've got are made by SunPower

- Trevor