If I remember correctly, Itunes has built in "CD" ripping software to convert songs from CD to mp3. The important thing to remember when ripping CD's is to choose a bit rate of at least 128 mb, no lower!
The smaller the number of "MB" the less space it takes(And the sound quality is degraded), the bigger the number of "MB" the more space it takes (The sound quality is better). I believe in the "Mp3" world 320Mbs is the highest you can go, but will be very high quality as compared to say 128Mbs. So unless your music collection is like, thousands of songs, you could always go for 320Mbs, I personally go somewhere in the middle with 192Mbs. Unless your an "Audiophile" you will never hear the difference between 320Mbs and 192Mbs. But start stepping below 192Mbs, there becomes a difference in noticeable quality.
I have songs that are 128Mbs, but the ones that are 192Mbs sound much richer and fuller (If that makes any sense).
Now we'll talk about the formats and my personal opinion. When ripping a CD, there's many choice like "ACC, Flac, VBR, Ogg" and then some. I don't personally use any of those and just stick with the plain old "Mp3" format because it is the most universal format most anything will play hands down. And that's something I learned because I have been through many devices.
Yes, devices nowadays support more formats especially the more popular ones, but I just stick with Mp3 format for reasons stated above. And don't worry, if you rip your CD'S to the full bit rate of 320Mbs and find your collection growing, you can always redo them at a lower bit rate, but the process can be very time consuming. So that's why I personally stick with 192Mbs.
This includes downloading music as well, I personally make sure it's in the popular Universal Mp3 format.
As far as memory? I always say "Get as much as you can afford"!
