Microsoft 365 features that help users manage their subscriptions, account settings, and billing information.
Hello Kozwe,
The short answer is Yes, we could have mixed plans in one tenant with 300 seats for Microsoft 365 Business Basic and 300 seats for Microsoft 365 Business Standard, and other users would be assigned with enterprise plans. For more information, please refer to https://www.microsoft.com/en-us/microsoft-365/enterprise/office-365-e1?activetab=pivot:faqtab >> FAQs >> Can I mix and match different Office 365 plans.
Please feel free to let me know if you need any further help, thanks.
Best Regards,
Oliver