The MacBook will require an extra 16MB VRAM (Intel) or more (NV) to run an external monitor even if the internal monitor is inactive. The MacBook hinge is designed so that when it is open, air is pushed up towards the screen; and when it is closed air is pushed under the hinge and out the back (you'll notice a 1/8th inch gap when the lid is closed) and as long as nothing is blocking the gap the air circulation will be sufficient.
But the air is pulled in through the keyboard. Won't closing the lid stifle that air flow?
But the air is pulled in through the keyboard. Won't closing the lid stifle that air flow?