OTW is for anyone who has an income of less than £60,000 a year. You'll qualify, I reckon?
So you're getting 6.5k a year, and 1k a year from the OTW...and your accommodation would come to approximately £3200 if you chose Roeburn.
That leaves you with £4300 for the year, which is £80 a week, say.
A typical weekly budget (I live off much cheaper) would maybe be:
£20 per week on food.
£20 per week on going out.
£20 a week on random other stuff (clothes, books, whatever)
Then you have £20 a week to save/use in emergencies, if you need it.
Of course, pick cheaper halls and you have even more money at your disposal.
Since Preston is such a small place, everything's pretty much together. The private halls that 2nd and 3rd years live in are pretty much on campus, and the houses are at most a 20 minute walk away. You've got one main road leading into town that's pretty much full of takeaways - great for when you're walking back to campus after a night out! - and pubs, cafes and clubs are dotted all around the city centre and on the outskirts of campus too.
Since everything's so close together, the only times you'll need to worry about transport are if you want to go bowling, to the cinema, swimming, or shopping at Asda, really - or of course if you want to get the train out of Preston!