1) Your Windows 7 license is very unlikely to be transferrable to your new computer as said, so I recommend getting Windows 8 64-bit OEM (and Start8 for $5USD to make the interface more like Windows 7, with the new interface still accessible.)
2) CPU: If you haven't yet bought that system I recommend getting an Intel i5-4xxx CPU instead and a suitable 1150 motherboard.
3) For DDR3 memory I recommend 2x4GB 1600MHz CAS9 instead of the single stick you have (run in Dual Channel to prevent any memory bottlenecks)
4) The Asus GTX750Ti is a very good card for the budget which can be overclocked even higher (roughly 20% more). Here's some benchmarks:
http://www.techpowerup.com/reviews/ASUS/GTX_750_Ti_OC/25.html
5) *Watch Dogs is a great game, but WAIT until the game has been patched. There's a major problem with the Video RAM filling up after which it starts stuttering massively. The company has admitted the problem and is currently working on it. It's really unplayable right now though.
6) YES, most games will run quite nicely on that system provided you properly tweak the settings to achieve your target frame rate such as:
a) 40FPS with VSYNC OFF, or
b) 60FPS with Adaptive VSYNC ON (force Adaptive VSYNC per game)