1. If I try copy it straight onto the 700mb/80 min CD-R there isnt enought "minutes" for all the songs (despite there only being 500mb)
When I tunes copies the files to the CD as a Music CD, it is the length of the song and not the file size that counts.
You'll always only be able to put 80 minutes onto a CD (or 72 if you've the smaller ones).
2. If I try copy them using the MP3 option, it tells me 70/80 won't be copied as they are not mp3's.
If you've ripped them with the default settings in iTunes, then they will be AAC format.
3. If I copy the music as just plain data most of the songs can't be listened to.
Unless your CD Player plays MP3's then you won't be able to do this. Also some play MP3's, but not sure if they will play AAC files.
Unless you have a headunit that plays MP3's you'll have to burn this music to a number of CD's.