Also. Does the internal fans produce enough cooling, or do I need extra cooling?
Also how does overclocking change the life of the Cube? Will it burn out sooner? Has anyone burned out one of these yet? Thanks!
I would suggest either removing the outer casing to allow for more airflow or adding a fan if you can. A small personal tabletop fan works in a pinch or obviously you can replace/add standard 120mm fans.
Cooling and overclocking stability go hand in hand.
For power supply choices, if for a single cube only, the XFX Core Edition PRO550W that was/is at Newegg recently for $26 after rebate is a solid choice. It's only Bronze efficiency however. If you plan to re-use the power supply elsewhere down the line or think you'll need additional features you might go a different route.
If you plan to add additional cubes a cheap Z750P and a
server-grade power supply interface board is really cost efficient.