I would start with the Ivy Bridge-Extreme platform that is coming out next month. It's the same socket as Sandy Bridge-Extreme(Socket 2011) so we have a good idea of prices and performance. Sandy Bridge-Extreme has a 4 core CPU(which isn't worth buying because you can build a cheaper system with a 4-core CPU with socket 1150/1155) and a few of 6-core CPU's. The entry level 6 core is the Intel Core i7-3930K and is about $530 on a good day. That is regarded as one of the best processors for the money, and Ivy Bridge-Extreme will be coming out with an equivalent CPU which is roughly the same price. That is what I"d go with for this build.
I would seriously think about not running 4 graphics cards........seriously. There are plenty of games out there that don't scale right with SLI so you'll potentially have 2-3 cards just sitting there while gaming. You also raise the chances of something not working correctly the more cards you have. Just something to think about.
32GB of RAM is no problem, as is the SSD. Socket 2011 motherboards with 8 RAM slots can hold quite a bit of RAM, so it's just a matter of what kind and how much. RAM isn't as cheap as it was 6 months to a year ago, so being realistic about what you need isn't a bad idea. You are looking at about $300-400 for a 32GB kit. The SSD is a no brainer for me. Samsung 840 Pro 256GB. Buy it and be done with it.
I have no idea what kind of water cooling parts you'll need, because an open loop system is more of a personal preference. There are 1000 ways to run a loop and it's something you'll have to figure out. You'll need to find a radiator that will fit in the confines of your case. You'll have to decide on a pump, what kind of fittings you want. Hoses or crystal link tubing, etc. My advice, check out this guy on youtube and you'll get a better understanding of what you can and can't do.
Singularity Computers
You need to make a choice on the monitors. Do you want to go with a 23/24" setup with 1080p resolution, or do you want to step up to a 27" monitor with 2560x1440 resolution? The 1440p resolution monitors are still higher than the 1080p by quite a bit sometimes, but there is no denying how awesome a display like that looks. Something to check out. Buying a good brand is the important part here.
If you want a very ballpark figure here it is.
CPU-$550
Mobo-$350
RAM-$350
SSD-$250
GPU-4 of any good card will be roughly $1800-2500
Water Cooling-No idea. I've never priced an open loop system, but you can bet it will cost a few to several hundred bucks
Monitor-$600-800 each for 27" 2560x1440 displays
That's the best I can do. Figure out your video card dilemma and we can get a better idea of where this is going.