good case and cpu cooler, the 10 core i7-6950x is rumored about 6 months out and compatible with x99. you wouldn't have to upgrade right then, but whenever you felt the need.
if you are looking for max stable overclock, and expansion like another video card, a quality 1k watt will be a better option. for a little bit more, the XFX P1-1250-BEFX and evga SuperNOVA 1300 G2 are on sale with rebates, if you don't mind rebates. the corsair hx850i is also just a bit more with its rebate, the hx1000i jumps up a bit with no rebate.
gpu - core to core count, the gtx 980 would be worth $400 vs the gtx 970 prices. the gtx 980 has more than just a core count difference, but it still makes the $500+ price tag unattractive. if you think you need more power right now, take a look a the gtx 980ti. if not, go with the gtx 970 and if/when you do need an upgrade, add another for premiere or upgrade to pascal or later, when nvidia releases.
if possible, i would avoid mirror or any raid for backup. raid (even mirror) can add an extra point of failure or data corruption vs isolated drives and data. three separate copies is good for critical data, two if not so important. using a cloud service can be a good option for one of the backup copies.
if you think you need more power right now, take a look a the gtx 980ti. if not, go with the gtx 970 and if/when you do need an upgrade, add another for premiere or upgrade to pascal.
Unfortunately the budget is not unlimited for me even this is pushing it a little... I am wondering tho, what do you mean upgrade to Pascal ? Sorry if it is a stupid question. First time i am hearing of this Pascal.
Also reading the forums i noticed some people say Samsung 850 EVO is not a good idea for OS and i should go with 850 PRO ? Is it worth the extra 50$ for PRO ?
pascal is nvidia's next gen architecture. its also a many months out, but its the next release vs current maxwell gtx 900 series.
there are a couple of points for evo vs pro series of the samsung ssd's. warranty length, reliability, speed, and endurance, the pro series are better in all categories. however, the os/apps drive doesn't need to be super fast, and may not see the amount of read and write cycles as compared to the media and cache drives. often a larger evo, say the evo 500gb vs pro 256gb, can overcome some of the speed and endurance, but is still leaves the warranty and reliability in question. samsung has been leading the way with ssd tech, and always shines in reviews and tests, so i personally don't worry much about the evo's. i think its a better chance most would upgrade for something bigger/newer/faster before it fails. if you plan on using it forever, the extra $50 for the pro might be worth the 10year warranty.
if you are still looking to buy parts, newegg has the hx1000i on its shell shocker sale today, good price with rebate...
If you are looking for max stable overclock and expansion like another video card, a quality 1k watt will be a better option. For a little bit more, the XFX P1-1250-BEFX and evga SuperNOVA 1300 G2 are on sale with rebates, if you don't mind rebates.