will oxford university accept potential students that want to take a gap year first?

-you’ll have to convince the tutors that not only are you good enough in the current pool of applicants you would still be good enough among next year’s potential applicants.

Physics, maths and engineering tutors tend not to like them as your maths will go rusty if you spend a year out without applying your mind to maths. see http://www.physics.ox.ac.uk/admissions/AFQs.htm#Yearout

http://www.maths.ox.ac.uk/prospective-students/undergraduate/admissions-criteria/

If your gap year has lots of maths related stuff they might allow a deferred place. They may give you maths to do over your gap year or they may only give you an immediate place.

For arts subjects I don’t think it really matters. Many of my friends reading history, PPE, english, etc. took gap years.