Tutor doing admissions for an Oxbridge college here. Comments based on my subject (PPE) but probably generally applicable.
To reiterate a few things:
4 A-levels definitely not required, or even an advantage really.
10A* GCSEs also definitely not expected unless the applicant went to a top school, or even particularly a strong advantage once other factors are taken into account.
Extra-curricular is not important, except for specific subjects as mentioned.
Yes it is easier to get into some colleges than others. However, the system is now designed to ensure that which college you apply to does not affect your chance of getting a place somewhere in the university, just not necessarily at your first choice. There are reallocations at various stages. I believe that for PPE it works pretty well these days - it didn't in the past.
And as for phoning up a college that rejected you after your results have come in? Good luck with that...
As others have said, there is plenty of information available on university and college websites as well as open days etc so please rely on those rather than anecdotes.