basic question hardware build

Hi everybody,

I wiil build a pc for wpa.
It will be around:
MB: 990fxa-ud3
2x 5870 to start, and go to 4x5870 few weeks later.
velociraptor 10k 150go (i got it, so use before invest in ssd later)

A.
-Is it secure to use a 'add 2 psu'? Exists reasons to be bad?
(I think use it when i get third and fourth 5870)

B.
-I hesitate 990fxa ud3/ud7 cause for 4 Graphic cards:
ud3 16x, 16x, 4x, 4x
ud7 16x, 16x, 8x, 8x
I didn't see thread about performance gain, it's 100$ difference$

C.
-How is ram important? I read that ram is not important, and i read that ram is important if big dictionnary.
I'm noob but i think understand:
-if mask: 2 or 4go are sufficient?
-if dictionnary: 8go or more?

D.
Which cpu to choose(in which case the cpu is important?)
I hesitate between:
-fx4300 95 Watts, 4 core, 3,80 GHz, 4 Mo (100$)
-fx6300 95 Watts, 6 core, 3,50 GHz, 8 Mo (120$)
-fx8350 125 Watts, 8 core, 4,00 GHz, 8 Mo (200$)

I used search function and not find.
I hope don't waste your time and this thread can be usefull for others.
Thanks to say me if something get wrong.