They generally trade blows but the 970 usually wins at 1080p but the 390 usually wins at 1440p, if you play alot of bethesda games then the extra vram of the 390 may come in handy for fallout 4 and maybe skyrim in some cases.
I think the tiles are fine, at least its not like win 8 anymore and if you dont like them then just get classic shell or whatever its called. I also think the live tiles are at least semi useful.
While agree that 3gb is the sweet spot right now, 4gb gives some headroom and some games can use it. What I find most interesting is that it says it has a 192 bit bus which indicates that it cant be gm 206 so maybe its a further cut down 970?
3tb drives have a really high failure rate, especially the seagate ones http://www.lifehacker.com.au/2015/01/why-you-should-buy-4-tb-hard-drives-and-skip-the-3-tb-ones/
The gtx 950 is a terrible value, unless that is your max budget dont buy it, spend 10-20 dollars more and get a 960. But between those two the 270 is a little better especially since you can oc it to 270x performance for free.
Just because its a gaming build doesnt mean it needs that many fans, my pc has 2 and its plenty cool. Even with overclocking you should be fine with just 3 fans, 2 intake and 1 outake is pretty balanced and having more will just make it noisier.