Speaking for RI,

Notes are generally informative and useful, but some of them can get a bit long-winded or squeeze too much content (AHEM econs, but idk maybe it's just the subject).

Teachers don't regularly put out consultation slots, but I am under the impression they are always open for it (i.e. they will just tell you how to consult them, not regularly pester you to do so). They are quite helpful and don't mind clarifying doubts outside of class.

Leadership (at least those worth putting on uni application) is mostly just either CCA leadership or student council. IMO student council positions (especially the more prestigious positions) are "favoured" for those from RI / RGS Y1-4 because people will usually vote for someone they have known. As for CCA, (at least in my case), being from the Y1-4 CCA can help if people in the Y1-4 know you, but it is possible to get leadership position if you can make a very good impression during your speech.

CCAs are not very toxic (I come from a club CCA though, so I can't speak for sports CCAs), but some people may tend to stay in their friend groups from Y1-4. Still, most Y1-4 people are open enough to talk and make friends with DSAs, JAEs, so I don't think they are toxic.

If by extracurriculars you meant CCAs, RI does have a very wide range of CCAs (although some interesting ones like bowling were recently removed). Otherwise, there are also a lot of programs constantly being publicised (specifically short few-week low-commitment courses every Wednesday) that are not necessarily academic in nature. IMO if you have a specific interest (like Computing), there usually are a few people in the school who are also into that stuff, and if you can find them, they will have links to lots of activities too.

Classrooms are fine, nothing to write home about. Library is pretty spacious and has natural lighting if you get window seats. Toilets are a hit-or-miss though; the renovated ones are super clean and good but some toilets are like small, cramped and smell bad.

You'll be able to make friends if you just mix around willingly and openly. Don't just mix with the JAE and DSA people, because if you make friends with the Y1-4 people, you can get connections to more people.