You may want to raise your budget to about 800 Euros. Each GPU block is going to cost about 60 to 100 Euro and you need four of those. Then lets say 150-200 Euro for the CPU Blocks. About 100 to 200 Euro for the Radiator[s], 100 to 150 Euro for the pumps (I think you would need more than one due to all the pressure created by these blocks) then all the barbs, tubing and I'd recommend a reservoir.. you're looking at about 800 euros or more I'd say.

One thing I figured out when I first got in to water cooling is that it can get expensive fast. All the little things like barbs soon add up when you are buying a bunch of them and there will be problems that require you to buy more stuff even the most well planned out build will have some issue and your build is going to be quite complicated and large.