Hello there!
Just a quick note - there is no 'campus' at Oxford - the University is an association of independent colleges (some 30 or more now). Within each college students took a set of rooms, identified by the number of the staircase.
Which college did he attend? Somehow I would be very surprised if it were not Christchurch (the largest, undoubtedly the most imposing and it does boast its own cathederal which is handy...). Once you know that, email the college whose archivist will be able to tell you which rooms were his.
Most colleges are open to visitors, to wander around, and are also very proud of their history. If you ask them nicely, they may let you peep inside - but someone may be living there.
London was (and is) commutable (50 minutes to London Padington now, and 1 20' then) but no student would bother to travel - after all, there are only three terms of eight weeks each year - so you don't need to spend that much time in the place.
I do hope you enjoy your trip - it's a most beautiful place to spend any amount of time.
Take Evelyn Waugh's 'Brideshead' to read for 1920's period feel - and Dorothy L Sayer's 'Gaudy Night' if you love a 1930's detective romance with a noble sleuth.