Congrats on getting 4 offers! I didn't study at any of the unis but I would personally choose between Edinburgh and Newcastle. Both cities are great to live in (I have lived in both) and the medical schools have a good reputation, with graduates doing very well in postgraduate exams. I don't know much about the course at Sheffield or St Andrews, but St Andrews is a tiny place with not much to do and I personally would have found it quite dull as a student.
With regards to doing a 6 year course - I think this is actually an advantage. I don't know about Newcastle or Sheffield specifically, but some medical schools only allow you to intercalate if your grades are good enough, so it can sometimes be quite competitive; if you are doing a 6 year course, you don't have to worry about this. Having a BSc will give you research experience and you will most likely get a presentation or even a publication out of it - these will also give you extra points when you apply for core and specialty training.
As for hospital placements in Edinburgh, these will be either at RIE or at WGH, however you may also have placements in Fife or in the Borders (you will be provided with accommodation for these). Public transport in Edinburgh is very reliable, so getting to placements shouldn't be an issue. Even if you finish really late (highly unlikely as a medical student!), you can easily get to the city centre from both RIE and WGH. I don't know about halls, but more senior medical students tend to live in Newington and Marchmont.