Pretty light, no more than 5KG. (Over estimating)
I have this https://www.asus.com/Graphics-Cards/TURBOGTX960OC2GD5/specifications/
It only just fits at 10.4 " x 4.76 " x 1.46 " Inch, 26.4 x 12.1 x3.7 Centimeter.
The card in this build is 10.5 " x 4.37 " x 1.5 " Inch, 26.67 x 11.12 x3.81 Centimeter
I think you would just be fine though.
If you got a 2.5 inch mechanical drive there would be. Or you could mount a 3.5 inch in the top and double sided tape the SSD to the bottom of the case.
You need that fully modular PSU in that case, from experience!
It's a jungle in there with a non-modular one :|
I get 40fps on lower settings on a 4 year old laptop with worse specs than this so gta v should be fine.
I bought a second hand xbox 360 for cheap ages ago, I still played on my (more expensive) computer because on the console I felt so limited. It will be nice when parts go back down in price, I guess it's a bad time to build a pc for the first time.
There are no matches for the PSU (I'm guessing in my country). This would be my first PC I build myself and am not sure what sort of PSU I would need. I'm in New Zealand if that helps.