Hey!
So firstly the membership - membership fees are paid to the JCR, which are then used to subsidise events and give money to different groups in Chad's (e.g. sports teams). I'm not really sure why Castle charges so much, but at Chad's we still have a number of events including multiple balls a year, a fashion show, a College Day, as well as lots of other college events, so I wouldn't say we offer less?
Regarding the vibe of Chad's - it is a very small college, so if you are looking to just blend in, it's quite difficult, as everyone knows everyone. However, I wouldn't say this is a bad thing as it's a great way to make lots of friends. We have a mixture of introverts and extroverts, and wouldn't consider ourselves a 'party college' (although we do have our moments). In Fresher's Week we make sure to offer both club nights out as well as nights in (e.g. paint and sip, murder mysteries etc) because we know not everyone will want to go out every night, nor stay in every night. So overall, you will find yourself knowing pretty much everyone in your year, and a lot of people in the years above, but that doesn't mean you have to be extroverted, it's just because its a small college - and being catered helps too because you'll see everyone at meal times.
Libraries - we currently have 7 libraries in college, so we are definitely one of the colleges with the most! They cater for a wide range of subjects, as well as English. We also have a great librarian who can help source books. You'll also find that Durham will give you access to a lot of online resources too, and I'm sure the English Department will also have a library (although I don't do English so cannot confirm this, but I would be surprised if they don't have a library).
Room sharing - 40% of rooms in college for first years are shared, so the likelihood is that you will get a shared room. Once you have a confirmed place at the college, after results day, the college will send you a form which will allow you to tell us about yourself (e.g. your daily routine, habits, hobbies, favourite music etc) and from there roommates will be matched together based on compatibility. So you should get someone with similar interests and routine to you, and we find the majority of roommates have a great time, and quite a few live in houses together in 2nd year.
Hope that all helps!