I think that I had 500 students in a class as a freshman at MIT, and that is a school where the entire freshman class was not all that much more than 1,000 students (I think that it is about 1300 now). Generally speaking upper year classes are likely to be smaller.
UCLA is a very good university.
I am thinking “master’s degree”. Whether this makes sense or not is likely to depend upon your major. It appears that you are in-state at UCLA, which suggests that over four years you might be saving enough $$ to pay for a master’s degree (unless you were offered very good need based aid at Penn).
Life is unpredictable. Sometimes you do the right thing for the wrong reason and it works out well. Sometimes something goes wrong, puts you in an awkward position, and you luck out (meet the right person, find the right job, …). I cannot comment on whether not wanting a vaccination is the right reason, but you appear to have ended up at a very good university where you are liking it and doing well. Being close to home can be helpful, and is likely to matter more for your bachelor’s degree compared to a graduate degree.
It sounds like you are doing very well at a great university that you like, and that is highly respected by both employers and graduate programs.