Hello!
For the open days and firm events, you don't need to go into detail about every session or presentation, as this can make things feel a bit list-like. Instead, focus on what you took away from the experience - what you learned about the firm's culture, practice areas, or working style, and how that helped shape your interests or career direction. I would perhaps briefly mention the main sessions of the event, but the focus of your entry should be about what stood out to you on the day. For example, mentioning how an open day clarified your preference for a certain type of firm or practice area tends to read much more insightfully than listing the day's activity.
In terms of how many WE entries to include, 9-10 isn't necessarily "too many", as long as each one adds value and you're not repeating the same points. It's fine to include long-term extracurriculars as semi-WE if they've helped develop relevant skills (e.g. leadership, teamwork, time management). Just make sure each entry has a clear purpose and shows personal growth or reflection - quality over quantity!
I hope that answers your question