Is this Gaming PC Build future-proof?

Just a tip, why don't you get a 2x4gb kit of RAM? It'll double your bandwidth for roughly the same price.

Depends on what time frame you consider the future. For instance, the gtx590 is one he'll of a powerful gpu, and it's not all that old considering. Yet sli is often a "future" upgrade possibility. Currently with SLI scaling in current games, power of a single gpu like a gtx970, SLI 590 just isn't worth it. For the price, SLI 660ti as compared to a gtx970 isn't worth it, and we are talking tech that's 3-5 years old.

The lga1150 is now a dead end. There are no possible upgrades. Of you decide to wait 3 years or so to get an i7-4790k, it'll probably cost close to what it costs today. A brand new i7-3770k is still over $300, laws of supply and demand.

The r9 280 is still a very popular card, yet it already has 1 successor in the r9 285, and now a 2nd in the r9 370/380, so what do you consider 'out of date'? If you equate that to the length of time the r9 280 has been out, your whole pc will be no different than a Sandy Bridge compared to Broadwell.

As many will tell you, there really is no such thing in electronics as' future-proof', all there is is get the best, fastest, strongest, most quality products you can afford, and hope they last a good long while, or at least until you are ready to upgrade again.

1. You can upgrade to an i7 or Xeon if available, at best.
2. Unknown. For all anyone knows, this latest batch of gpus maybe the last/best in pcie x16, and 2 years from now motherboards may see pcie x64 slots. Kinda like trying to upgrade from AGP to x16. Just won't.
3. Adding more ddr3 ram in the future may or may not work. Not all silicon is compatible, not all identical kits are compatible, secondary and tertiary timings will differ, that can and do often result in non working ram when mixed.
4. Unknown. A case is just a case, gpus and coolers may get bigger or smaller, or may dissappear entirely in favor of an msata or pci express style card. Who can say for sure?
5. 5 years ago, the biggest gpus required huge amounts of power, then along came Maxwell, and changed the world. 5 years from now, the biggest gpus may only require a 500w psu for sli, so, who knows. You may never need a bigger psu, wattage wise anyways. For all I know, ppl may be working on a new standard, making ATX obsolete, of which psus will be 1/2 the current size, with twice the capacity.

Nothing is "future proof".

1. Processors are restricted by their socket compatibility. The answer to your first question is possibly. The 1150 socket, the one you selected, will end one day. Intel is releasing a new socket this year along with new processors (Skylake 1151). At that time, they will begin to slowly cease production of 1150 CPUs. Will you be able to upgrade to an i7 in the future? If you can find one that is compatible with your motherboard, yes.

2. Graphic cards are pretty easy to swap out. So yes.

3. As others have stated, you can add more RAM but it's doesn't always work. Mixing kits (regardless of voltage or speed) can pose issues but it's sometimes possible to overcome these issues.

4. Case will be fine.

5. Yes you can but remember, build quality is more important than wattage.

well
first, if the cpu is with the same socket, yes, you can upgrade to i7 if need
and , I dont think there will be any problem to upgrade the graphic cards

and, you are using the non-k series cpu
so if you are not going for the overclocking
use h97 will be good as well, which like msi h97 gaming 3
but if you do want to upgrade the k series cpu in the feature
get msi z97 gaming 5