you have to check here before going to amd crossfire...http://www.guru3d.com/articles_pages/ultra_high_definition_pc_gaming_benchmark_review_uhd,12.html
it look like amd have a serious problem with the crossfire rig
but about your questions... you will be able to run BF4
i've read it.
paid attention as much as possible.
you already have an fx6300. afaik, there will be bottlenecking with crossfired 7950 even if you o.c., in cpu-demanding scenarios. online multiplayer games may tax it to it's limit.
crossfiring 2x 7950 (or starting with any multigpu combo) might not be a good idea. you would be better off starting with single 7950, then moving up after amd fixes crossfire's most of crossfire issues. amd has already taken the first step, but they haven't fixed everything. they're gonna launch new cards soon, btw.
o.c. - swiftech h220 may be good. it's semi-customizable aio cooler. other alternative... cm hyper 212 evo is always a cheap, good choice.
overclocking is a journey (as wise people say) not a goal. every cpu is made differently. your cpu will o.c. differently from others.
can't offer further help.
Thank you, btw I wouldn't buy a 2nd card for maybe 5 months or so. I'm going to start with one as I don't have the cash yet. Like right now my next move is RAM, then PSU cause I have an old GeForce 210 and 430 Watt I'll use until I get the GPU and PSU
EDIT and my fear is I like to wait before buying new products even when they come out because I have bad luck with buying new products that tend to not work like they should