How much Power supply is needed here?

Hi guys, new here...I'm setting up a new pc, sooo a few questions here.
I'm planning on getting an Asus A88XM-plus motheboard, Amd X4 860K cpu and Sapphire R9 280 3GB video card...so how much power supply would be enough...450-500W?..would 650 be an overkill? Is all of this fully compatible?
Do I need a sound card, modem or special cooling or something? ( I already have 2*8gb Ram sticks and HDD, don't really need DVD drive).
I'm also thinking in between Antec 902 V3 case and a lot cheaper LC Power Gaming 975b Air wing Midi...how much quality difference is there in between these two?
Also, how much improvement is there in between this card and my current one, sapphire r7 265 2gb?
Are there anything that you would exchange for something else...I'm on a tight budget, but I don't mind spending a few extra bucks if it be worth in the long run.
Thanks in advance.
 
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