Yes. Graphic card memory and system memory have nothing to do with each other. You can use a GDDR5 graphics card on a motherboard that accepts only DDR3 system memory.
Yes you can when it says ddr3 on the mobo that's just for the motherboard ram. The gddr5 is graphics memory on the graphics card itself so it doesn't effect the mobo it effects the GPU's internal memory controller
Yes you should. If you are running a high end card you would be lucky for that system NOT to start. If it did it would most likely blow out. I'm assuming it's a cheap OEM PSU. Go for a quality 600 watt Bronze plus. Such as Seasonic, Corsair, or EVGA.
If you get a more powerful card then you'll need a better power supply.
Well.. I bought my GTX750Ti ASUS for $140 and now.. I'm confused.. How am I going to change my PSU..
And what PSU do you think I should upgrade to..
My current PSU is Dazumba 380W