1 It is in Zone 4 of Northwest London, should be fine 2 Take a train from Marylebone train station in central London to Bicester North, or try to find whether there are coaches to Bicester in places near you 3 Yes, should be. But pay attention that London underground is now closing down all ticket offices to save expenditures. If that happened in LHR underground station, I am sure there would be staff helping you buy correct ticket/oyster card via the self-service machine, as London Underground says they plan to send the ticket office staff 'more visible' at platforms or in stations to help passengers.
2 Take a train from Marylebone train station in central London to Bicester North, or try to find whether there are coaches to Bicester in places near you
3 Yes, should be. But pay attention that London underground is now closing down all ticket offices to save expenditures. If that happened in LHR underground station, I am sure there would be staff helping you buy correct ticket/oyster card via the self-service machine, as London Underground says they plan to send the ticket office staff 'more visible' at platforms or in stations to help passengers.