1. No first year has to share. I don't think you even get the option as a fresher. You'll obviously be able to check out the other accommodation before second year.
2. 10 minutes walk, maybe less, assuming they're at the engineering faculty (computer science ones aren't till second year)
3. This will vary so hugely, dependant on you, I'm not sure it's worth coming up with a generic figure. If there's a more specific cost you're interested in...?
4. Many, probably the large majority, do. You really don't *need* one, so it's your choice.
5. Not so much. Normal formal is in gowns, but in a modern hall that wouldn't look out of place in a new build school. Guest nights are black tie, application only (to ensure fairness) meals in the rather more characterful Old Hall. You can always go on swaps to other colleges, of course. :-)