Don't go with AMD's APU's if you're planning on doing a pretty hardcore gaming build like this. APU's are for budget gaming builds. If you're getting a Radeon HD 7970, you're going to need a more powerful CPU to drive it. You should at least get an AMD FX6300. An FX8350 or i5 3570K would be even better.
Also, Arctic Silver 5 was the best thermal compound around the year 2008. It no longer holds that title. Not to mention that it is electrically conductive, so if you get it anywhere but between the CPU and CPU cooler, you could potentially short something out. I would recommend getting Arctic Cooling MX-4 instead. It's not conductive, and it's the best performing stuff on the market. You should be able to get a tube of it for around $10. Not to mention that MX-4 has no cure time whatsoever.
No problem. The APUs are more designed for budget level gaming rigs, which means you're usually working with a budget between $300 and $500. They'll be able to run games at the bare minimum settings, but they're not really meant to be run alongside a flagship GPU. The APU would just bottleneck it.
It might a little, but I don't think you'll encounter a significant bottleneck with it unless you're running more than one graphics card. Make sure you're getting an AM3+ motherboard with it too, because that FM2 socket motherboard won't be compatible with it.
Its not the ram thats getting overclocked, you have to change the BIOS setting for ram so that it accepts 2133. If you dont then it will probably underclock the ram to 1866 and you wont have the 2133's performance. (hope that makes sence)
You won't really need that speed of ram. Only APUs benefit from that. You could buy some 1333Mhz or 1600Mhz ram instead. It'll save you money, plus it might help you get off some problems. Sometimes, faster ram speeds won't work, and they will throttle down to slower speeds. So it's like it stole money from you. I also recommend getting a bigger case. The V3 is small IMO. 7970s are huge, especially the Gigabyte versions. The least I would get is either the Zalman Z11( can fit it with 5mm of space remaining) or the CM Haf 912( you'd have to remove the removable hard drive bays). I'd recommend getting a Corsair 200R or 300R, which can fit them easily. All of them are relatively cheap.
If you want to find great deals, go to pcpartpicker.com. They list computer parts, each with different buying options( Newegg, Amazon, etc.), all of which are reliable, and they list the seller's price from lowest to highest, so you'll be able to find a great price.
Lastly, if you're planning to buy some aftermarket thermal paste, then you should also buy an aftermarket cooler. I recommend the CM Hyper 212 Evo, which is great for people on a budget( as low as $25).