Hello there! I'm a First Year Bsc DS student here at Bristol who is currently procrastinating instead of revising for my Exams. So naturally I'm the most qualified person to answer any questions you may have considering I might be joining you next year lmao.
Data Science is run by the School of Mathematics. We share about two modules with other mathematicians (including Comp Sci + Maths or Phy + Maths etc) and Economics students. For these lectures, you will be at times attending massive theatres/halls with up to 400 people rife with fresh's flue. Don't worry lectures tend to dry up pretty quickly when everyone realises replays exist.
The two shared modules are Stats & Prob and Analysis. Additionally, we have two units that are catered to us "Matrix & Linear Algebra" and "Mathematical Tools for Data Science"(Calculus). University Math and high school math are different. I can't guarantee that even though you enjoyed your A level you will enjoy Data Science. Conversly, you might enjoy the course even though you hated your A levels. I find this particularly true for stats.
There are also two extra programming units. One in C++ and R covering algorithms and concepts like Vectorised code vs Scalar code; and the other unit is a unit provided by the School of Science called Introduction to Scientific Computing where they introduce libraries like Pandas, Matplotlib and Numpy in Python. I personally had the most fun with these. If you've done any kind of programming on your own time or are familiar with basic concepts that you may find in your A level you'll be fine. Most students however did struggle to grasp C/C++.
Lectures vary in quality. Analysis is a notoriously tricky unit for students fresh out of A levels / IB. Your lecturer can make or break how you feel about it. Unfortunately for us, we had a poor lecturer at the start. That being said, the second half of the unit was done by the best lecturer I've had so far Dr Lee Butler(bless his sole the man can read minds). Sometimes lecturers have no concept of how ignorant we are. They tend to go on tangents or give way too much detail. The correlation between a good researcher and a good teacher is very slim. Often I find it may even be inversely correlated. I think they are mostly fine but my prespective is obviously limited. Ultimately it comes down to you how well you perform.
When it comes to socialising, I think joining some societies might be a decent idea to find like-minded people. There are also plenty of events like bar crawls and whatnot you can attend to meet new people. Bristol has a pretty neat night life, as I'm sure you are aware. If you like going clubbing I'm sure it won't disappoint.
Good luck with your A levels and hope to see you in Bristol.