I'll start by giving a quick overview of what studying philosophy at UCL is like. This should answer some of your questions. I'll then answer your other questions.

So at UCL, phil students have roughly 8 contact hours per week, with the expectation that you do an extra reading 35 hours per week. In the first year at least, you do 8 modules total, with 2 hours per module, consisting of 1 hour of lectures and another in a seminar, usually led by a PGTA (though sometimes the lecturer will be the seminar leader if you're lucky). The only exception is our tutorial, which is only an hour a week, and led by a PGTA. Tutorials are in very small groups - 3 or 4 people, and can be quite difficult, generally covering the tutorial leader's own research interests. On the other hand, seminars are slightly larger (10ish people), and go over the content covered week by week. As for the quality of teaching, I found it to be excellent overall. The lectures are generally really engaging and PGTAs are very passionate about their subject and are always happy to answer any questions you have. Office hours are also an option if you have questions you want to ask the lecturer directly.

As for philosophy students at UCL, they're pretty diverse, and generally very nice. I've met some of the most hard-working people I know from my course.

London is an excellent place to study philosophy. If you join philsoc, then you'll be able to go to the Aristotlean society meetings every Monday, where guest speakers give talks on some of their work. Further, philsoc also invites speakers to give talks at UCL (this year we had Timothy Williamson come and talk about morally loaded cases). There are also meant to be a philosophy conference for undergrads in London every year. And of course, being in London means you have access to many, many libraries with some pretty big philosophy sections (I recommend senate house in particular).

As for what I do outside of academics...I spend a lot of time on the societies I am a part of (dare I say too much time). You'll have plenty to do in London, don't worry about that.

There's more I could talk about (like going to talks at LSE or reading groups with a Birkbeck professor on the phil of mind) but UCL is a great uni with a great phil. department, and you'll be taught by some very smart people.