Firstly, don't ever start a PhD because you "want to be a student again". PhD life is nothing like a normal undergradute student life. It's completely different, it's more like a full time job with a lot more hours. Also, I wouldn't suggest starting one just because you are bored of your current job. If you want to do a PhD find a topic/subject that you are passionate about, and are willing to spend 3-4 years on a tiny part of it. If you can't do this, then there is a very high probability that you'll get bored of the PhD very quickly and end up quitting.

I too lived in postgrad halls for my first year and it wasn't a great experience. Although the students in the building were generally easy to live with, nearly all were international students mainly from China. Again, nice people, but they had no interest in mixing with anyone but their own type. So overall, it was incredibly difficult to socialise with anyone, due to their poor English and unwillingness to mix. As a result I left the halls after a few months and got a shared private flat. Although this was more hassle in terms of bills, repair work etc.., it's much better in the long run, as you get a chance to meet your flatmates beforehand.
So overall, if you're thinking of halls, make sure you have an idea of the type of people you are going to be living with.

I did exactly that! I went travelling to Australia and Asia straight after my undergraduate degree, and applied for (science) Phd's in the UK while I was travelling in Oz. As for the interviews, I did them by telephone. It was no problem, as long as you don't use a mobile. Anyway, everything went well and I got myself a fully funded PhD . I am now in my second year of the PhD and everything is going great, so no regrets what so ever!
In fact, there were many people applying for postgrad courses while travelling, although most were applying for Master degrees to do when they got back home.
Anyway, I definitley say go for the gap year, It will be great! I'd love to do one again. In fact, I'm sort of planning another one after I finish my PhD