Are my GCSE's good enough for Cambridge?

Thank you very much!

And also, you get to apply to five different courses (unless you're applying to medicine, then it's slightly different). So for mine, I applied for Physics (MPhys) at Oxford, Durham, Exeter, Lancaster and York. I was pretty sure I'd get offers from Durham, Exeter, Lancaster and York , so I didn't mind using the fifth one to apply to Oxford It didn't matter that I probably wouldn't get a place because I knew I'd end up with at least three other offers, so it was worth taking the gamble.

How can I get any AS levels, if I'm not doing any exams in year 12?

You will have to rely on a very good performance in Y12 and getting good predicted grades for your A-levels. That might get you an interview, and then the interview together with the Cambridge Law Test may get you an offer.

Realistically no: not because Cambridge particularly care about GCSEs, but because the sort of individual that populate its Law course (and indeed, that of virtually any Russell Group Magic Circle clearing-house) would not achieve below A* in History, English Language or English Literature—essentially, subjects which reward elementary analytical and rhetorical flair—unless they were suffering from acute head trauma at the time of the relevant exam.

Of course, I should hope that the above salvo of derision only cements your resolve to prove me wrong.

You made a good choice by choosing to study the subjects which you did well in at GCSE, as when looking at your GCSEs they will care more about what you got in your most relevant subjects. However you said you are targeted ABB, however you will need to get AAA at AS to be competitive AND will need to be predicted at least A*AA. It's not impossible, I know of people who have gotten into Cambridge (and Oxford, believe it or not) who have gotten in with 3 or less A*s, and even no A*s. It's not about being good at everything, it's about being amazing in the specific subject you want to study.

Saying that, you want to apply to Law. With these kind of competitive courses like Law and Medicine, being good at everything is kind of important, whereas in something like Physics they would only care about how good you are at physics and maths. Therefore I'm not sure you would be a strong applicant. Are you sure you want to do Law? Have you considered other courses based on your A-Level subjects e.g. History, English, Philosophy, or Theology? Law has 5 apps per place while Theology only has 2 and History has only 3.