Need Advice Upgrading My Ancient Rig for 1080p @ 120hz Gaming

[MoonDoggy-X]

Thank you in advance for anyone's advice and patience. I know there have been a lot of questions like this so I'll get straight to the point. I am just getting back into gaming on my computer as of recent. I pretty much missed the past 5 years because I moved to an area with no internet. I built my current computer about 6-7 years ago, and it consists of...

PCU: Intel Core 2 Quad q9550 @2.83ghz
Cooling: OCZ Vendetta Heatsink w/fan
MOBO: EVGA nForce 750i FTW Motherboard
OS: Windows Vista Home Premium 64bit
RAM: 4gb PC 6400 DDR2 SDram @ 800mhz
Storage: WD Black 640gb HDD
PSU: 650 Watt PSU(don't remember the make)
Case: Cooler Master HAF Case
GPU: EVGA GTX 960 Super SC (formally GTX 285)
Monitor: Vizio 32" 1080p/120hz TV hooked up with HDMI

I know I am in need of some MAJOR upgrades and I plan on building a new system before the end of the year. Right now, I mainly play Star Trek Online, but I want to start playing Inquisition and a few others. When I first got back on STO, my GTX 285 showed its age. I replaced it about a week ago with a GTX 960. The game looks a lot better, but I'm not getting the 120fps I want that give the display its depth. I'm not worried about 4k gaming yet because I don't have a 4k monitor.
All I'm worried about is gaming at 1080p @ 120hz for now. So my questions are...

1) Do I need to upgrade the CPU and RAM to get the frame rate I want, or will running 2 GTX 960s in sli do the trick?

2) If so, can my current system even handle running 2 GTX 960's in sli? I already know I's have to replace the PSU because I wouldn't have enough connectors?

3) For old and new builds, would I just be better off with a better GPU even though I already bought one GTX 960?

Pretty much, I'm asking if I can get what I want from a $300 upgrade(GPU/PSU) or am I forced to go for the $1,000+ full system upgrade to meet my goals? I know I can build a good system for under $1,000, but If I'm going to invest, might as well make it future-proof. Again, any points in the right direction will be greatly appreciated. Thanks.

 

[APliskin]

1) Yes, you will need to upgrade the CPU and RAM, at least to 8GB DDR3 1666mhz.
2) Your PSU will be fine, 2 960s won't draw more than 600W even OC'd.
3) Me personally, I would not have gotten that 960, rather I would have gotten a 970.

You'll probably need a new full system, grab another 960 and SLI it.

 

[MoonDoggy-X]

1) Yes, you will need to upgrade the CPU and RAM, at least to 8GB DDR3 1666mhz.
2) Your PSU will be fine, 2 960s won't draw more than 600W even OC'd.
3) Me personally, I would not have gotten that 960, rather I would have gotten a 970.

You'll probably need a new full system, grab another 960 and SLI it.

Thanks for the advice. The reason I say I'll need a new PSU for sli is because the GTX 960 uses a 8-pin connector and my current PSU only has one 8-pin and one 6-pin PCI power connectors. Do you have any suggestions on where to get reasonably priced components? Or brands, good or bad? Been out of the game for a while. I started looking up EVGA, but it doesn't look like they're much in the under $200 MOBO game anymore.