Office 365 Group Limits

Below is a table that shows Office365 Group limits as of March 2018.

Maximum	Value
Owners per group	100
Groups a user can create	250
Groups an admin can create	Up to default tenant limit of 500K
Number of members	More than 1,000, though only 1,000 can access the Group conversations concurrently. Users might notice delays when accessing the calendar and conversations in very large groups in Outlook
Number of Groups a user can be a member of	1,000
File storage	1 Terabyte + 500 Megabytes per subscribed user + any additional storage purchased. You can purchase an unlimited amount of additional storage.
Group Mailbox size	50 GB