|Your video card choice will set the size power supply you will need.|
Always select a power supply with a single 12Volt rail, 80% or greater efficiency rating (certified), Active PFC, Sufficient Wattage and 12Volt Amperage for any possible video card upgrades, a Quality name brand, a longer warranty period.
You need at least a mid-tower case, without its own power supply, sufficient internal and external bays, USB3 and other front ports you may need, and reasonably high consumer ratings (read many reviews to see if there is a trend in the complaints). Look at placement of switches, external ports (bottom mounted USB ports are useless if you keep the tower on the floor as are top mounted ones if you keep it on the desktop or high shelf), and make sure you will be happy with the look of the case.
You have to be a little bit crazy to keep you from going insane.