Office Group membership limitation

My two cents here:

There is no limit to the number of Groups per Office 365 tenant: Incorrect, the limit is 500.000 Groups per tenant, even it could be possible to create more
Each user can create up to 250 Office 365 Groups: correct
Each user can be a member of up to 1,024 Groups: correct
Groups with over 1,000 users are supported: correct. Indeed current limit (not documented) is 2500 users / group
Group conversations can be slow in groups of this size or greater: It depends on what you understand by group conversation. Remember conversations in Groups happens in the Group Inbox that is just a EXO inbox
Public Groups can be a risk, since anyone in your organization can join them: if the group is created as public, I think there is not a risk at all
A special Group mailbox is created in Office 365 to store all the Groups content: Partially correct...when a Group is created, an  EXO mailbox is created for storing Group conversations and a SPO site is created to store Group documents
The maximum size of this mailbox is 50 GB: Correct, the size for each group mailbox is 50 GB

More information here: https://support.office.com/en-us/article/learn-about-office-365-groups-b565caa1-5c40-40ef-9915-60fdb2d97fa2#ID0EAADAAA=Manage