I usually have enormous!! notes (being summaries of all the cases, readings, legislation, practice questions etc) more so for a security blanket than anything, don't really remember actually using these huge notes. But I am one of those people that would rather waste time preparing them, as I remember content better if i have read it and re-typed it out myself, and I don't want to over summarise notes and find that i actually needed them. That whole better to be safe than sorry approach
The notes that i actually use however are usually about 10 pages per topic for more difficult/complex units, 5 pages or so for the easier/less complex units, very spaced out, large-ish font, all bullet points so it's easier to read quickly. "Theory" style units are much, much less though, i usually have 30 or so pages total as I personally remember theories and history better than I remember details of statutes and cases so in the 'practical' units i do need more notes just in case.
It's more a matter of how your notes are structured and organised than how long they are. Some people do really well with one page per topic, some people do really well with hundreds of pages, it all depends on what makes you comfortable. But i wouldn't recommend at all doing what some people do of bringing in 'essay style' notes, being blocks of text as its too hard to read quickly in an exam.
Also - get your notes bound if you can as I've seen so many people drop their folders or get the pages they had clipped together muddled up and they end up wasting a lot of time trying to re order them or find them - binding avoids that problem. Plus, if you have crappy small desks for the exam its easy to keep it all together on the desk