Streaming Netflix offline on Macbook using Windows
I think by memory you mean disk space - that really depends on how many movies and other files you want to store at a time.

There should be no difference in video/audio quality. The only exception is if you're running something else that is so taxing on the computer that it is not able to play the video in real time. If that happens, close down the other programs while watching video. This is no different than when streaming Netflix on a PC.