Hey, I'm also a Sheffield pro (going into third year when we get back uuuuughhh) so I guess I can answer any questions you have too!
I was in Endcliffe and I got really unlucky with my flat, I was in an all-male 6 person flat with only four people, two of whom were foreign students (from Nigeria and Malaysia, both were Muslim... as interesting and great as they were, they're not the sort of people who want to go out with you 3 or 4 nights a week!) and one who was a PhD student. I made really good friends with the flats next door and above and had an amazing time in my first two years, so even if worst comes to worst you'll be fine!
Sheffield's nightlife is fantastic. It's not like Manchester or Leeds, a massive sprawl of super expensive and super busy places, but there are loads of places to go (Leadmill, Plug, the Academy, Carver Street, Corp, Replica, DQ, every bar down West Street... probs give Embrace a miss though
), all of which have amazingly cheap student nights... you won't get bored here. I've got mates in pretty much every major 'night out' city across the country and I haven't visited one with a better atmosphere (or cheaper drinks) than Sheffield. The nights at the union are ok, but don't get into the routine of going there every time you go out - there's so much more to town than the union!
And don't worry about 'not being clever enough' or anything... there's alot of Oxbridge rejects and snobs who think they're well above little old Sheffield uni, and just as many who you'll see in exams who you've never seen turn up for lectures before who scrape through every semester! The lecturers are generally great and everyone knows they're in the same boat so don't worry and work yourself into the ground - it's your first year at uni and you only need 40% to pass, so no panicking! As long as you vaguely keep up with your reading and hand everything in on time, it's super easy to stay afloat... compared to A level, first year uni workload is nothing.
Other than that I do English and play football and all that stuff, so feel free to ask me stuff!
Ben x