Congrats on your offer to study at Lancaster. If you did end up going with your top choice I hope you love it.
Since you already have an idea of the rankings for all the universities I think the best thing would be go give you some insight on the campus and general life at the uni.
For one, postgraduates have their college on campus, basically where most postgraduates would live if they didn't live off campus. Owing to that there is a large focus on events that postgraduates would enjoy and benefit from held by the college. There are also a large number of international students in graduate college and it would give you a good sense of community and home.
I would say that the Lancaster University campus is very beautiful and it was a major factor in why I chose to go to Lancaster. In terms of student life, there are a lot of events hosted on campus during term time and also socials that are held off-campus in the town that students from all grade levels are free to attend. The nightlife in Lancaster itself may not be the most lively, but something I found makes up for that is its proximity to a lot of different cities, where you could easily hop on a bus or train for more vibrancy if needed, while still having a nice calm study environment.
I hope this helped a little, albeit being a bit late.
Goodluck with your uni experience.
Lancaster University Student Ambassador.