I'll post my actual build specifications below, but I'm just trying to look ahead here to what would be a feasible upgrade without having to break any banks. Pretty casual gamer myself, but I like my rig to have some ass behind it. I currently have a GTX 660 by Gigabyte, and I totally enjoy it;but I can tell in the next few years it won't be standing up quite as well for the new titles and I want to start considering some of the options I have for upgrades.
The FX-6300 is good for most things. It is pretty fast. With that motherboard your upgrade options are limited but maybe an AMD 8 core down the line if you feel you need more CPU power.
As for a future upgrade for your GPU.
The GTX 970 is great and well priced although if you don't really play too many hardcore titles than it may not be worth it.
The R9 280 and 285 are good choices as well. They are cheaper but still quite powerful.
Right now it is a little hard to say. Once more nVidia 9XX cards come out and we see what AMD does with the R9 3XX series it will be easier to give a recommendation.
Depends on how much you want to spend, honestly. You can pair anything with anything for the most part. As far as pure performance per price, the 290 at $300 is king, though the 970 is a good option as well. For future cards, we won't really know until they come out (looking forward to the 3xx series myself).
As far as what gpu would give you a balanced build though, that one is harder to say. You can always upgrade in increments, meaning that you get the best gpu that you can afford when the time comes and if you find that the cpu is lacking, then upgrade that next. With the 6300 though, a balanced gpu would be hard to call. Many games don't really care what cpu you have at all, and if you plan on playing at 4k in the near future, the cpu should be the last thing that you bother with. But, with a 6300, at 1080p, I would look at something with about as much power as a 280x, or likely a 960. Beyond that, and you are likely to see a cpu bottleneck in many cpu demanding games (especially ones that require good single core performance). Though a bottleneck really isn't as big of a deal as people make it out to be. If you bottleneck your gpu with a poor cpu, then you know where the cpu tops out, and you can upgrade that when you have the money and move on from there. Really not a big deal at all.
I have heard some people say that it is better to buy everything all at once than to buy things incrementally. Personally, I went with increments, but if you get everythign at once, you aren't going to see performance degrade (with newer games and higher resolutions) between purchases. The value of the gpu you bought will likely decrease before you are able to buy a new cpu, etc. It is up to you though.
Yeah the 280X (7970) will still max pretty much every game at 1080p. It is a great deal. You can find them for sub $200 sometimes. Plus you get free games with AMD.
GTX970 are great then there are cards that should be on firesales at the moment - 780, 770, or 290, 280x. Pretty good time to be buying a gpu actually, some bargains to be had since the 9xx series has been priced very competitively. 780's here in oz were going for $250AU the other day from a major outlet. Shop around and price match, haggle.