Upgrading Dell XPS8300 to GTX760

Currently I have a Dell XPS8300 with:

Intel® Core™ i7-2600 Processor (3.40GHz, 8MB)
12.288 MB 1.333 MHz Dual Channel DDR3 (2 x 4 GB / 2 x 2 GB)
1.25GB NVIDIA® GeForce® GTX 560 Ti  GDDR5

After searching this forum and several others I came with the following hardware to replace/add:

Corsair XMS3 CMX16GX3M2A1333C9  (2X 8GB)
MSI GeForce GTX 760 2GB Gaming (N760 TF 2GD5/OC)
Corsair AX760

Now would my main questions be: Would this be possible or would I run into problems? I'm not very familiar with hardware specs and system requirements.

Also I'm wondering if this would be a profitable upgrade in order to run games more smoothly? I can imagine the hard disks are still a big bottleneck?

If I replace the 2GB RAM modules for the 8GB mentioned above, is this going to work? I suppose it should give me total 24GB.

Is the graphic card going to work with the bios/motherboard and does it fit in the Dell’s XPS8300 case? Also I’m wondering if this is not causing temperature issues?

Is the PSU going to fit? I’ve read something about most power outlets of standard PSU’s are not fitting into the case of the XPS8300?

Thanks for your replies!!