Settings for students

I'd agree with most of the posts above.
I recommend disable the creation of teams for all users using the relevant PowerShell Script
https://support.office.com/en-us/article/Manage-who-can-create-Office-365-Groups-4c46c8cb-17d0-44b5-9776-005fced8e618
Use SDS to create Class Teams and design a specific structure for staff Teams for administration with appropriate permissions.
https://docs.microsoft.com/en-us/education/get-started/use-school-data-sync
The new Teams admin center allows more granular controls and you can enable certain features for certain users.
I'd disable private chat and audio and video calling for students.
https://admin.teams.microsoft.com
Initially I also disable students from editing and deleting their own chat messages so if they post something inappropriate the teacher can take a relevant screenshot to follow standard discipline procedures and then delete it.

I recommend do not allow posting in general channel and change permissions so files can not be edited in general channel. If this is required create a different channel that can be easily deleted.

I use channels as subgroups because my students work in groups for the year, initially we gave students global permission to private message but have since turned this off, they can still post in conversations in the Team general conversations and the different channels and they use @ to alert someone if the message if for a particular person. Also have permission to delete and edit their messages.