Sure, they'll work together, but I'll make a few recommendations.
A 2x8GB memory kit would probably be better than a 4x4GB kit. Same total capacity, but a little less strain on the memory controller and it leaves more memory slots for upgrades later on.
The newer FX-8320 is a little faster than the FX-8150 and uses less power, but is usually about the same price if not cheaper, so it's better to buy the 8320 than the 8150.
A good Radeon 7770 such as the Sapphire Vapor-X, Sapphire OC, or XFX Black Edition will roughly meet the 6870 in overall gaming performance while usually being cheaper and using much less power.
DDR5 is is mistake on the website, it's actually GDDR5. That's the type of memory on te graphics card, don't worry, it has nothing to do with the system RAM and is simply one factor in the graphics card's performance. GDDR5 is the fastest type of memory used by consumer graphics cards right now.
I think the 7770 is slightly below/almost equal to the 6850. I doubt it comes close to 6870, but would like to see benchmarks if you have one in mind.
The 7770 was slightly below the 6850 with drivers from like eight months ago. Current drivers such as the most recent beta for Catalyst 12.11 are much better and even back then, 7770s such as the three that I mentioned have very large factory overclocks and could nip at the heels of the 6870. Now, they can meet or even beat it. Hold on, I'll see if I can find any up to date benchmarks.