If you plan to use it as a 24x7 download rig, I would suggest to spare some cash as for a seperate download device. The savings may not be immediately visible, but the power savings surely will start piling up in about 2 years to equate the cost of the device.
Rather than getting a 1x8GB stick, its better to go for 2x4GB as they are cheaper vis a vis the 8GB ones. Plus you get the benefits of dual channel.
Instead of Z77, you could go for a B75 based board and save some cash.
Rather than the Seasonic, I think Corsair would be a better choice.
What are you planning to use as a monitor?
Another point to be noted is that if you plan to go for the AMD card, certain games are included as part of a bundle. That may not make it attractive, but its a plus surely.