Explanation
This permission setting should be checked if the custom CRM object is not available in New Data Stream configuration. The user who connects the Salesforce CRM connector must have View All permission for the custom object in the source CRM org.
References:https://help.salesforce.com/s/articleView?id=sf.c360_a_data_cloud_salesforce_crm.htm&type=5

This operator can be used to create a segment for a birthday campaign that is evaluated daily. It compares a date attribute to the current date and returns true if they have the same month and day, regardless ofthe year.
References:https://help.salesforce.com/s/articleView?id=sf.c360_a_data_cloud_segmentation_operators.htm&ty

The type of the Event Time Field while ingesting Engagement data should be Immutable. Immutable means that the field value cannot be changed once it is ingested. The Event Time Field is a mandatory field for Engagement data that represents the timestamp of when an event occurred. It is important to keep this field immutable to ensure the accuracy and consistency of the event data. Reference: Engagement Data Model

This feature can integrate in real time with Salesforce CRM. Data Actions allow you to perform actionson Salesforce CRM records based on Data Cloud data, such as creating, updating, or deleting records.
References:https://help.salesforce.com/s/articleView?id=sf.c360_a_data_actions.htm&type=5

Explanation
The maximum number of calculated insights that can be created per tenant is 50. A calculated insight is a metric that defines and calculates a multidimensional measure on your data. You can use calculated insights to create segments and analyze your data in Data Cloud. You can also use calculated insights to create dashboards and reports in Tableau CRM. References: Calculated Insights