Question about motherboard and CPU compatibility with windows 7

Windows 7 does have limitations in terms of what hardware in can support. Fortunately those limitations are confined for the most part to multi-cpu environments and CPUs with more than 256 cores, so you have nothing to worry about - any 32bit or 64bit CPU will be compatible with Windows 7. This is the system requirements page for Windows 7: http://windows.microsoft.com/en-US/windows7/products/system-requirements

The motherboard and the CPU must have matching socket types, and the memory (RAM) you choose must be of the same type as the motherboard supports (DDR3 / DDR4 are both equally prevalent now, but no motherboard to my knowledge supports both types). The GPU will present some compatibility considerations too, specifically whether the motherboard supports crossfire and whether the PSU can provide them with enough power.

As far as CPU recommendations go, 1080p gaming isn't too affected and from PCs I've built in the past anything from quad core AMD CPUs like the FX 4000 series or the i3 4370 upwards don't cause an FPS bottleneck in a majority of games. From what you've said you're after solid performance, so I would recommend looking at something like the FX 6000 series or, a better option, an i5 4690K as a starting point. The better the CPU, the faster the game can do a lot of the logic processing (like AI and loading things) - you want it to be good enough that it is always ready to process environment changes and pass instructions to the GPU.

Fury Xs are smaller than the average GPU (most mATX or ATX cases will be alright) but they do have an external 120mm water cooling block / fan, so any case you choose will have to have a nearby 120mm mount for the radiator. In your case two Fury Xs might be a little overkill insofar as 1080p / 1440p gaming goes. I'm not the best person to ask for a GPU recommendation as I have only limited experience with AMDs line, but my single R9 290X is capable of running every game I've chucked at it in 1080p/60fps/ultra. It's also capable of eyefinity (5760x1080) at 60fps on high / ultra for most games too, so I imagine a single Fury X would serve you just as well as two (and save you £500 you can put into other components). From looking at benchmarks, the Fury X can handle 4K games nicely, so 1440p should be a breeze

Hope that helps! If you have any specific hardware in mind, let us know and we can confirm whether it's compatible for your system or not