(This is the best advice you'll get off TSR)
No amount of A*s at GCSE will guarantee you a place nor an interview dependent on the course you're applying for with the exception of competitive courses such as Medicine etc.
- Definitely apply as long as you get okay AS results if that's what you want
- if you have decent AS Levels apply to Cambridge who on the whole do not seem to care as much as Oxford for GCSEs.