Box 1: Yes

You can assign additional account administrators in the Azure Portal.

Box 2: No

You need an Azure Active Directory account to manage a subscription, not a Microsoft account.

An account is created in the Azure Active Directory when you create the subscription. Further accounts can be created in the Azure Active Directory to manage the subscription.

Box 3: No

Resource groups are logical containers for Azure resources. However, resource groups do not contain subscriptions. Subscriptions contain resource groups.

References:

https://docs.microsoft.com/en-us/office365/enterprise/subscriptions-licenses-accounts-and-tenants-for-microsoft-c loud-offerings