Congratulations on getting a place at Oxford. Going to Uni can seem a bit daunting but there will be lots of fellow freshers in a similar position. Freshers week is there to help you orientate yourself and answer many of the questions you may have. It's also a great opportunity to begin making new friends. For financial questions most of the banks in Oxford have friendly staff who can guide new students through the banking system.
Oxford is all about independent learning and you will need to develop time management skills, to juggle your work and social life. If your course is essay based (Arts&Humanities) then check out essay planning strategies. Some but not all Colleges have a study skills tutor who run sessions on making the transition from school to Uni. Oxford's short terms means that study time can be intense, so I would suggest joining a couple of sports clubs or societies for some downtime.