Field-Level Security (FLS) is a fundamental security feature in Salesforce that allows administrators to control access to specific fields based on user roles. This feature is crucial for ensuring that sensitive customer data is only accessible by authorized personnel, thereby providing a targeted approach to data security and compliance. "B. Configure field-level security to restrict access to sensitive data based on user roles" is therefore the most important security requirement for managing access to sensitive information effectively.
Reference: Salesforce Field-Level Security

The Data Migration Assistant (DMA) tool is specifically designed to analyze data formats and compatibility, making it an essential resource for assessing data readiness prior to migration. It helps in evaluating how legacy data formats will translate into Salesforce, identifying any potential issues like data inconsistency or incompatibility early in the migration process. Therefore, "C. Data Migration Assistant (DMA) tool for analyzing data format and compatibility" is the most effective tool for assessing legacy data readiness.
Reference: Salesforce Data Migration

When Omni-Channel routing is activated on a queue for the first time, existing records in that queue will not automatically be pushed to agents. This is because Omni-Channel only starts routing work items that arrive in the queue after its activation. Any work that was already in the queue prior to enabling Omni-Channel will need to be manually reassigned or triggered to enter the Omni-Channel routing process.

Monitoring and validating automated case escalation effectively involves using multiple tools that offer various insights into the process:
A: Monitoring Escalation History related list within case records helps track escalation triggers and actions, providing a direct audit trail for each case.
B: Utilizing reporting tools to analyze trends in case escalation provides insights into frequency, reasons, and potential areas for process improvement.
C: Supervisor Console offers real-time insights into case statuses, including escalations, enabling supervisors to oversee and adjust processes as needed.
Combining these tools provides a holistic view of case escalation effectiveness and helps in identifying and implementing necessary adjustments.

For Ursa Major Solar, the KPIs to prioritize to measure the success of the Contact Center implementation, given their goals to enhance customer satisfaction and streamline costs, should be average handling time, number of calls answered, customer satisfaction score, and employee training time. These KPIs directly align with improving service efficiency and quality. Average handling time and number of calls answered focus on operational efficiency, customer satisfaction score measures the impact on customer loyalty and satisfaction, and employee training time helps in assessing the effectiveness and speed of preparing new agents, which impacts both costs and service quality.