you should get at least a 600 watt psu and most importantly DO NOT GET ANY CHEAP BRAND PSU u will regret it. i recommend you get a 650 or 750 watt psu from brands like xfx or corsair and seasonic. make sure tat the psu is at least 80 plus bronze. below 600 watt sometimes u may have trouble with the computer due to insufficient power from psu when playing games tat need alot of juice. i have a radeon 7870 with the corsair cx750 psu and it works great.
Where are you coming up with that? You can Crossfire 2 7770's with less than 550W. One needs about 450W.
Performance degrades slightly over time on a power supply so you'll want a good brand and one that's a little more than you need. Cheap brands of power supplies will degrade very quickly and usually they can't even supply the wattage that's advertised. A good power supply will last you a decade or longer but a cheap one won't last 3 months. I'm someone who has been through this before.
That is an absolutely fantastic power supply. It will definitely do.
As far as the cooler goes I would recommend a hyper 212 evo but I don't know if it will fit because I don't know what case you have. The cooler is very tall.