It’s possible to do, but you’d be juggling a lot and, honestly, it would probably be an awful year. You would be balancing your 4 a levels and EPQ alongside all of the work required for an Oxford application like wider reading for the PS, admissions tests, and the interview- while trying to find time to relax, go out with friends, maybe get a part time job to save for uni. Have a look at the entry requirements for the course. It’ll most likely be 3 a levels with high grade requirements. By taking on so much you won’t have as much time to revise and you may find your grades become more diluted, whereas if you focused on the 3 you’d have some more time. Many people successfully apply to Oxford with 3. Good luck with your application!