Hi there!
In my experience, the majority of student houses do also have locks on the doors so I wouldn't worry too much. Multiple flatmates that I have had have brought PC setups and had no issue at all. Regarding getting a laptop vs renting it, my only concern would be when renting, you have to be able to get in relatively early to get one as in my experience, they can go quickly. However, I would say, even if you weren't able to rent a laptop, you can always write notes on paper and then go home and rewrite them on your PC, which is something I find can be good for recall as you're actively going over the lecture content again. A laptop is definitely not a mandatory thing if you have access to some form of computer.
Hope this helps!
Jen (UoS student rep)