Not just an app, but honestly I get all of this and more out of my nextcloud instance. There are mindmap plugins you can download as well as good task support that’s well integrated with however many separate Calender’s you want, etc. Its great!
The only downside is that on the mobile side of things you end up with a whole bunch of apps to sync and interface with the instance (nextcloud, etar, tasks.org, nextcloud notes etc)
where do you plan to go to start that off after school?