Most people have this weird fantasy about "freshers" as if it is a mixture of prom and the in-betweeners movie
It varies from uni to uni and can be longer or shorter but is basically a week of trudging around a campus to register and find facilities, join clubs and explore before term starts.
There are booze fuelled trips organised ( some unis stamp down hard on them now due to complaints) at the same time as say the CU organises a "meet and greet" prayer session with tea and biscuits .
Being a uni and in the UK, booze will feature but not necessarily in everything
Dress sense is an individual thing. Some types like clubbing , some students like sticky floored pubs and heavy metal. Be yourself, but be willing to go along with the vibe.
Generally first years dress in clothes that their parents approved of, and are clean and tidy
Towards the end of year one, going into years two, it goes a bit haywire as funds dry up and standards slip. I knew one guy who wore a blue boiler suit all of year 2 because it was easy, cheap, and he didn't have to decide. Come year three people tidy up and start to look employable
If you have a couple of "nice outfits" that will do
Bear in mind that you are cleaning your own clothes so bring stuff that isn't all dry clean only and can mostly be bunged in together