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Save up for the GTX 970 the performance and VRAM will be worth it.
Also 600 more than enough for the 970 and a i7, a lot more. Most single card setups don't use more than 450 watts.
The Corsair 200r/300r are good cheap options for cases. The Phanteks Enthoo Pro, the Corsair Air 540, and the Corsair 750D are what I've seen get recommended a lot these days.

Just go for the beast of a card that is the GTX 970, a lot of people are saying it's the best bang for the buck. The 980 isn't to much of an upgrade to warrent an extra $250.

That power supply is fine, mot people these days overestimate how much power a gpu can draw. You could almost run two of that, without over clocking of course.

While the 970 is a nice upgrade from the 760 (which is a good card already), the 980 is NOT worth the extra money over the 970.
970 vs 980

(EDIT: mistake in the following paragraph, 2x970 NOT recommended for your PSU)
Should you need more performance, you could pick another 970 in a year, when it will cost a bit less.
Your motherboard has a secondary PCI-E 4x slot. A 16x/4x SLI would have less performance than a 8x/8x setup, but it would still be way better than a 980.

Coming to PSU and case. The GTX970 has a lowish TDP (125W, vs your current 760's 170W!), which means that your PSU is perfectly capable of feeding it. It's also of a good quality, not even consumption spikes would bother it.
In fact a 600W gold certified PSU can handle a GTX970 SLI setup as well. (<- same mistake again: do NOT SLI 2x970 on your PSU)

Low TDP also means low heat generated. Unless you really want a new case, you won't need it: if it handles the 760, the 970 will stay cooler.

Techspot's take on GPU-s
Basically same conclusions as stated before

I personally have the Fractal Design Define R4 (there is also a window model, I have the windowless). I picked it because it is silent and it is very silent. I have 2 x R9 270x crossfire setup with i5 and I only had to replace the stock cooler for the CPU (that s*** has some high frequencies under load). It has two fans and I removed one of the HDD cage for better airflow (didn't really need it). I also have an audio card in there so it is pretty tight around the GPU-s, but the temps are very nice around 55-68C (I usually switch the case fans on higher voltage to keep the GPU-s cool during intesive gaming sessions and keep them on low voltage for normal use). I'm a fan of minimalism in design

Sorry i'm hijacking the post, but i just have a simple question and i don't think its worth another post

How are Amd GPU-s made by xfx? I'm looking at this and this is it worth it, or should i get a Sapphire or maybe Gigabyte card for ~50$ more?

Any opinion on the manufacturer would be nice since i saw one guy buy those for a benchmark comparison video so i hoped they aren't bad

Important addendum. From my exchange with Desidiosus 2 things came out:

1) a stable SLI with 2x970 is not possible with your PSU.

2) A single card will indeed be handled with no problems, but you'll have to follow one small detail. Despite the low TDP of 145W, the GTX970 requires 24A (for consumption spikes). Your PSU has either 20A or 18A for each 12v rail, so when you connect the 2x6pin connectors, you'll have to make sure they come from 2 different rails.