Solid build overall. To answer your questions:
1) 650 watts should be plenty. The trend in both GPUs & CPUs (the most power hungry components in a system) has been downward in power consumption. So if anything your next GPU/CPU will use less juice than the one you're currently putting in.
2) For gaming you really aren't going to see much of a benefit going from an i5 to an i7. The majority of the games out there struggle to use the 4 cores of an i5 as is let alone start using the hyperthreading that an i7 provides. Stick with the i7 you have. edit
I just noticed in your original post that you mentioned that you do video streaming/processing. Now the i5 can still handle that however if you do heavy amounts of video streaming & processing on a regular basis then I would say it is worth it to step up to an i7.
3) You might need at least one SATA cable for the HDD since the SSD should come with one since it looks to be a retail packout. You might also get one with the motherboard but it doesn't state whether it does or not in the description. Better off paying the buck or two for a cable and at worst have an extra sitting around.
4) The case you linked comes with two fans, one for the intake and one for the exhaust.
There are two changes that I would suggest for your build:
1) Swap the Visiontek for a Gigabyte 7970 3GB
as the cooler is a much better design and you save a few bucks in the bargain.
2) Cases are largely a personal choice but I've been impressed with Fractal Design's offering's as of late. For the same price as the ThermalTake you could get a much better designed (at least IMO) Fractal Design Define R4 Titanium