Why did you select that guy as best answer lol
The 3570 is a previous generation, Haswell is newer, and for the same price, slightly better.
Why 16GB of RAM? When gaming, you'll see around 3.5-4.5GB of usage, and 8GB is plenty for photo editing, and even light video editing. But by all means, get 16GB if you want lol
500w is more than plenty to power a non-overclocked CPU and 760. You'll probably have around 300w at max load.
mATX is generally cheaper, yes. And unless you plan on having 7 expansion cards, there's no real reason to get a full size ATX board except for looks I guess. You can't SLI on an H87 board (not that you would with a 500w PSU anyway), which would leave you 5 or 6 expansion slots empty for no reason. But again, it's your money, do whatever you want lol