Just what the title says.
Not really.
Make sure its atleast 1600 MHz, Dual Channel.
If budget is a problem get 2 sticks of 2GB instead.
But DEFINITELY get Dual Channel.
yeah give priority to RAM if you are buying APU.. the iGPU will have noticeable impact if you purchase better RAM
8 GB Ram for apu is ideal. Also, as mentioned by everyone, the difference between 1333 MHz and 1600 MHz can be quite visible in an apu.