One PSU is more than enough just make sure it is not some lightweight grey import. I would suggest a PSU of 750W from a reputable brand, When selecting PSU, find out where the RMA centre is, if you do ever have a problem think of the cost of shipping the defective item to the RMA centre.
RAM with the X77 chipset is good to go with pretty much any brand of ram. Unlike the X79 platform which seems far more picky. It is best to get one kit if you want to populate all four slots however.
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