I always sigh a but when someone says their dream is to attend a certain institution. Your dreams should be about what you want to achieve (ultimately a reputation is built on success stories the name is simply a badge for it). I always think prioritizing institution over personal goals may well lead to an underwhelming university experience.
Id say a school which gets 2 or 3 students into Oxbridge per year is doing very well (of course it’s also about proportionality to student body).
I find your description of your GCSE performance somewhat irritating. Id think if you have achieved the GCSEs you present you should be able to contextualise your performance a little better- they are excellent, essentially in old money 9x A*/A & 1x A/B which is obviously excellent.