1. 400R is good but usually there are better options for the price, like Fractal Design Define R4.
2. I'd probably go for a Samsung 840 250GB or a Corsair Neutron 256GB on that budget.
3. No, GTX 770 is perfect for 1920x1200. Although I would say the 7970 is usually better bang for buck.
4. You'll probably like Logitech G400. It's not for me but if you find Logitech mice comfortable, why risk a change.
5. I have a Logitech G710+, it's pretty much perfect with the exception that the paint falls off pretty easily, I've only used this for a couple of months and my S and D keys don't look anything like S an D anymore. If you don't mind about such cosmetic faults, I can definitely recommend it. I haven't tried any other mechanical boards.
Is there a
Microcenter near you?
I would stick to ATX and keep open the possibility of going SLI/Crossfire. A 1440p monitor will like a SLI/CF setup, and your budget is big enough for this. I would also prefer to be able to OC the CPU in order to minimize bottle necking with such a powerful GPU setup, it can be something you do later when needed.