@Anjana R Thanks for reaching out.
1) There is no device management policies which gets applied when you join it to Azure AD. For that you will have to use Intune portal and setup Auto enrollment to Intune if you want this. (Auto Enrollment makes it easier )
2) Yes, multiple users can login with their Azure AD account on the Azure AD Joined Devices.
3) Yes they can be directly enrolled in Intune either when they are Azure AD joined or even when they are not Azure AD join.
Here are few links which will help you further :
- Different Methods to Enroll the Windows machine to Intune : https://learn.microsoft.com/en-us/mem/intune/enrollment/windows-enrollment-methods
- Managing Windows 10 with Intune : https://www.microsoft.com/en-us/insidetrack/managing-windows-10-devices-with-microsoft-intune
- Planning Azure AD join Deployments : https://learn.microsoft.com/en-us/azure/active-directory/devices/azureadjoin-plan
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