|"How much memory should be on the PCI express Card for Video"|
How much memory for what? Normal everyday use? HD video? Video editing? Gaming? Each has different requirements & it seems a lot of people focus on the memory amount. Certainly memory is a factor in choosing a card, but the GPU used on the card is much more important.
I wouldn't get a card with less than 512MB but 1-2GB seems to be the new standard amount. Higher end cards have 4GB or more. Pay attention to the type of memory & the memory interface (buswidth). DDR3 or GDDR3 memory used to be the way to go but GDDR5 is currently the best. And sometimes manufacturers play games with the specs to try to sucker you in to buying an inferior product. For example, look at the comparison of these two 2GB GT 730 cards. If you just look at memory, you might think the one with 128-bit DDR3 would be better. But if you look at the GPU specs, the 128-bit card runs at just 700MHz with 96 CUDA cores vs the 64-bit card which runs at 902MHz with 384 CUDA cards. The EVGA 64-bit card is better but the weaker MSI card costs more.
EVGA GT 730 2GB vs MSI GT 730 2GB