1) Depends on how big the Peltier is. If it only just covers the area of the heatspreader then you could get a way without a coldplate, but if it is bigger than the heatspreader then a coldplate is essential.
2) It's always better to use a separate PSU.
3) Depends how cold it gets. Try it with just what you mentioned first, and if any exposed areas start to get cold, then use more insulation.
P.S. Are you sure an 80W Peltier is enough? How much heat does your CPU put out?
|