Sheffield is no scarier than any other university town or city in Britain. Like any city there are areas that you'd want to avoid but I lived there for ages and never had a problem. Sheffield also has excellent folk clubs and sessions and the university has a vibrant ceilidh society and plenty of excellent musicians to play with and learn from; plus they go to lots of festivals so you're bound to run into some of them if you go to festivals (look for ceilidh soc t-shirts).