Require a little help here.

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How important is the cpu for gpu cracking? Should I get like a cheap dual core or a good quad core.

I would suggest going with a solid mid-range CPU, for two reasons. First, you likely will still do some CPU cracking. For example, straight wordlist attacks against fast hashes are faster on CPU than GPU, bcrypt is still faster on CPU, and scrypt with large memory requirements is impossible on GPU. Also not all algorithms have been implemented on GPU. Second, you will want a decent CPU for doing things like wordlist manipulation and potfile management.

How much ram would I need and does the ram speed play a role.

You should have at least as much host RAM as video RAM. So if you have four GPUs with 4GB of vram each, then you should have at least 16GB of host RAM. RAM also helps when doing things such as wordlist manipulation. RAM is cheap, there's no reason to skimp out.

If I have the 4x graphic card set on the mobo, would a 1000psu be sufficient or I will need at least two psu?

Depends on what GPU you buy, but no, in general a 1000W PSU would not be enough to power a quad-GPU system, nor would it likely have enough PCI-e power connectors for four GPUs.

You'll have to do the math once you select your GPUs, but there's really no reason not to go with the biggest and best PSU you can find. I'm quite partial to the EVGA 1600 T2 and Lepa G1600.

A good power supply is cheap insurance. If your PSU can't keep up with demand, you will find yourself buying not only a new PSU, but also likely a new motherboard as well.