Thanks for your help, and I have one more question  in the end

@Wassupia
The monthly profit has many factors which cannot be measured, but I'm willing to take the risk also because of ideological reasons. 

@Treggar, @Wassupia
I think I found this PSU in reasonable price - "Seasonic M12II-750 Bronze 750W" which I hope will do the work

Regarding hardware:
I have a question regarding the m/b I planned to buy:

I will start with end - my question is:
Can I connect the 7950 to a m/b with PCIe x1, and still get the highest hashrate of this GPU?

Explanation:
I've checked with the store, and the available m/b is this one:
ASUS H61M-K
https://www.asus.com/Motherboards/H61MK/#specifications

It says it has the following slots:
1 x PCIe 3.0/2.0 x16 *1
2 x PCIe 2.0 x1

And I planned to use it with the following CPU - "Celeron G470"  (bcz its the cheapest this store sells)
From here it says that Celeron will not utilize PCIe 3.0 -
http://forums.anandtech.com/showthread.php?t=2316826

And anyway I planned to put 2 GPUs, so I need to use one x1 slot.

So back to the question -
Is this will decrease the mining hashrate ?
Should I look for a m/b with 2 slots of x16 ?

Thanks for your help !,
J.

Hi,

I plan to build my first "mini" rig.
The plan is to run on linux, via usb stick

The hardware I plan to buy:
(Based on "cheapest" I can in the store except for GPU and PSU)
=====================
1) GPU = 2x "Sapphire 7950 3GB GDDR5 HDMI RETAIL DUALX with Boost"
2) CPU = 1x Intel Celeron Dual-Core G1610 2.6Ghz
3) MB = 1x "Intel® H61 Chipset" Gigabyte\MSI - (store: "Whats in stock"), from what I saw the Gigabyte have "1 x PCI Express x16 slot, running at x16" and "2 x PCI Express x1 slots"
4) MEMORY = none
5) HDD = none
6) PSU = Seasonic watts

Questions
=======
1. Any general comments\advice, anything I need to check/look for ?
2. I'm confused about the PSU, I saw the GPU draws about 225 watts each, but in AMD's website they recommend 500 watts and even 750 watts PSU for 1 GPU.
"How many watts" should I get for 2 GPUs ?

Thanks a lot for your help !,
J.