I think you should definitely e-mail or phone your supervisor to ask for details of the arrangements for your first week - I'm sure they won't think this is an unreasonable request! As for coming and going when you like, well, things may well be different in other research groups but in the group I am working with, research students are expected to attend every working day (unless studying elsewhere) and to work full-time hours (at least!). In my experience post-grad research bears little resemblence to under-grad degrees! Good luck :o)