Question New HDD - cable confusion


Dec 8, 2015
Hey guys,

I am thinking about getting a new HDD lately... I decided to probably go into Seagate Barracuda 2TB
but since I didnt build my computer myself back in the day I am kinda confused in the wiring in the back of the case
the new HDD only has a SATA power connector but the cables from my PSU are 4 pin MOLEX only so my questions are:
Can I use a reduction from the MOLEX 4pin into SATA powe cable?

Which cable from the PSU do I use? because I currently have one SSD + one HDD so I am adding a second HDD and my current HDD+SSD are plugged into the SATA (1?) cable coming from the PSU so they are both connected to one cable... but I am assuming that plugging the third one into the same cable may be a problem so can I use the SATA (2?) cable which powers the optical drive? Or could I use the PERIF1 cable for the third HDD?

I am really confused with this so I d appreciate any help... also I dont have much access to the PSU itself so I cant really see which cable is SATA1, SATA2 etc but I think that shouldnt really matter right? But I for sure know which one is PERIF1...
I hope the picture helps...
One more thing - I will move the SSD to the location a designated and use the its original location in that ´´shelf´´ for the new HDD since there is no other place to put it