Firstly: Have I been a complete idiot and chosen components that are incompatible with each other?
Everything should work together.
Secondly: From what I have read, the power supply should be about right. Am I mistaken?
I'm running a similar system (i5-760, 6970) from a 500W power supply. 650 is more than enough.
Thirdly: 1333 MHz RAM vs 1600 MHz. Will I notice a difference?
Not much of one, but it's measurable. Above 1600MHz is a waste, so get 1600MHz if it doesn't cost more. Additionally, don't spend more to get better/tighter RAM timings - it doesn't make much of a difference on Sandy Bridge. Is that PC-16000 memory, or is it 1600MHz memory? PC-16000 is 2000MHz memory (16000MB/second), DDR3-1600MHz is PC-12800.
Also: If you're gaming, you probably won't notice the difference between 4G and 8G. You definitely won't notice the difference between 8 and 16. It's not a lot of money, but why spend more than you have to? (Things may be different if you're doing lots of heavy-duty database stuff, or scientific modelling, or running lots of VMs. But for a gaming machine, 8G is more than enough).
Fourthly: Will the H100 fit in the top of the case (it has mounting holes for fans), and should I get fans to fill the rest of the fan mounting points?
H100 should fit (the specs claim it'll fit a 120mm x 240mm rad in the top of the case). Again, though, I have to ask: Why bother? The all-in-one water coolers are no better than the higher-end air coolers, from what reviewers claim, and they are more expensive. Secondly, you won't need that much cooling unless you're going for some monster overclock, and gaming performance is far more reliant on the GPU than the CPU. Personally, I'd recommend getting a cheap, good air cooler (Coolermaster Hyper 212 Evo is amazing for the price), and save a good 70 euros.
As far as fans go: If you were going for Crossfire or SLI (if you shave enough money from the above, two 560Tis or two 6950s are amazing; if you're willing to deal with the problems that a multi-GPU setup can have) I would put an extra intake fan in on the side, over the video cards, to give them fresh air. Otherwise, one front and one back should be fine, and adding more later is easy enough if you find it's necessary. It won't be at stock speeds, but it could let you overclock more, or it could reduce the noise from the system (lots of big fans spinning slowly is quieter than a few spinning fast).
