The security setting 'Enable Username and Password for Web Services' allows users to access the API with their Marketing Cloud username and password. If this setting is deselected, users will need to use an API user or an installed package to access the API

For NTO to format links for Google Analytics 360 without including PII, they should use non-personally identifiable information in the query string parameters. Suitable options include:
A). Product Code: Identifies a product without revealing customer identity.
B). Application ID: An internal reference that does not disclose personal details.
C). Subscriber ID: A unique identifier for a subscriber that is not directly tied to personal details like an email or name.
Reference: Salesforce Help - Personalization Strings and PII

When creating a data extension for subscriber data from a data warehouse, fields that typically require minimal consideration for size or scalability include:
Number: Fields designated as 'Number' generally consume less storage space and are straightforward in terms of scalability and processing within data extensions.
Boolean: Boolean fields, representing simple true/false values, are highly efficient in terms of storage and processing, making them less of a concern in terms of scalability.
Reference: Salesforce Marketing Cloud Data Extension Best Practices

The entry source types for Journey Builder include:
C). Data Extension, Email List, API Event, Date Based EventThese sources allow a marketing campaign to automatically start or transition contacts based on their interaction with various data sources:
Data Extension: Contacts can be injected into a journey based on records in a data extension.
Email List: Contacts from a specific email list can be used as an entry event.
API Event: This allows external systems to trigger entry into a journey.
Date Based Event: Contacts can enter a journey based on a specific date or a date attribute in a data extension.
Reference: Salesforce Help - Journey Builder Entry Sources