Inspiron 530, more GPU questions

I have asked a few GPU Questions in the past

Here are a few more-

what is VRAM? is that the same as RAM?

DVI vs HDMI- which is the better choice?

HDMI- can a GPU output audio with the video signal? i know that DVI is video only.

How is one able to determine the maximum capacity GPU your system can handle?

How much RAM (or VRAM?) do i need? match my system? (8GB)

Can the 3.5 drive power cable power a GPU?

System is Inspiron 530, with the Core 2 Duo 2.2Ghz CPU, 8GB RAM 800Mhz. i know i can replace the motherboard to from (GM002) to the GM003 which can handle a Quad Core CPU. And i  know that the stock PSU (300 Watts) needs to be upgraded. would 500 watts be enough? or too much?