Skwoad

You will see a huge improvement upgrading to a 970/290 from a gt 9600, it is really up to you what card you want to get, neither of them will disappoint.
If you can wait to June, have a look at some of the benchmarks for the r9 300 series, they look like they will be very competitively priced  

In terms of performance, the 970 will out perform the 290 in both 1080 and 1440p by a small margin, Im not sure what the prices are like were you live, but the 290 is $400~ and the 970 is $500~. If you want best price to performance go for the 290, if you want to get those 5-10 fps on the games go for the 970. One of the biggest differences that are present is the heat output of each card. The r9 290 can get quite hot, but that should be much of an issue. 
Not sure if this applies to you but, the 970 is alot more energy efficient as well.
DSR is done through GForce Experience (Nvidia Desktop App), it lets you change your res. to a DSR res. and therefore making the game render at 1440p / 4k. When in the game you can then change the res. from 1080p - 1440p with ease
Edit: Clarity
Yes the 1440p res will be available on a 1080p monitor, however this is only available on the 970 as the r9 290 does not support this
And no the 970 does not beat the 290 by far, however I own a 970 and am very happy with it  

If you are really want to future proof it, either go for a 970 or wait until June for the release of Fiji gpu's.
There will most likely be a small price drop on the current gen r9 200 series when they are released, so it might be worth waiting it out
Apart from that the build looks great (y), And to what @dizmo said, the resolution that you will be gaming at helps decide what gpu you will need
Edit:
Just out of curiosity, what are you going to be doing for storage? 

Ahah, I would love to have speakers but mic is too important for me D:

Thanks alot for the really detailed responses, you help is highly appreciated.