In the context of a project that involves new technology and an experienced Scrum team, the most suitable estimation technique is using story points. This method allows the team to leverage their collective experience and familiarity with each other's work to estimate the effort required for tasks relative to each other. Story points reflect the complexity, effort, and uncertainty of the task, making them ideal for projects where the technology is new and exact estimates are challenging to produce. Since the team has a history of successful collaboration, their established velocity can help predict how quickly they can work through the backlog.
The use of story points is supported by Agile methodologies and is a common practice in Scrum teams for estimating work effort. This approach is detailed in the Agile Practice Guide, which is a complementary document to the PMBOK Guide, provided by PMI for understanding Agile practices in project management. The choice of story points over other estimation techniques is also consistent with the principles outlined in the PMI's Professional in Business Analysis (PBA) Reference Materials, which emphasize the importance of leveraging team expertise and past performance to inform project estimates.

When a project experiences schedule delays, especially with tasks on the critical path, it is crucial to review the critical path with stakeholders. This collaborative review helps in understanding the impact of the delays and in defining the next steps to mitigate the issues. The stakeholders, including the project team, suppliers, and sponsor, can provide valuable input and decision-making power to help navigate the issues1.
References:
PMBOK Guide - Sixth Edition2.
"19 Frequently Asked Questions on the Critical Path Method" by Praveen Malik, PMP3.
"Exam PMP topic 1 question 321 discussion - ExamTopics"1.
"Five Tips for Being Prepared for Supply Chain Disruption" - PMI.org4.

Before implementing agile methodologies, it is crucial for the project manager to evaluate the organization's culture and readiness for such a transformation. This involves understanding the current processes, mindsets, and capabilities of the team members and the organization as a whole. Agile methodologies require a significant shift in how projects are managed and require an environment that supports collaboration, flexibility, and rapid response to change. Without assessing these factors, the transition to agile may face resistance or fail to be effectively integrated into the organization's practices.
The answer is supported by the PMBOK Guide principles which emphasize the importance of tailoring project management approaches based on the context and environment of the project12. Additionally, the Professional in Business Analysis Reference Materials suggest that understanding the organization and its readiness for change is a key aspect of business analysis, which is integral to successful project management34.

According to the PMBOKGuide, the project manager is responsible for creating a project charter that defines the project purpose, objectives, scope, and high-level risks. The project charter also establishes the project vision, which is a clear and concise description of the desired outcome of the project. The project vision provides a common understanding of the project goals and benefits among the project stakeholders, including the product owner and the agile team. The project manager should share the project vision with the agile team at the beginning of the project and ensure that it aligns with the product owner's expectations. The project manager should also facilitate the definition of the team ground rules, which are the agreed-upon norms of behavior and expectations for the agile team. The team ground rules help to create a collaborative and respectful team culture, foster effective communication, and resolve conflicts. The project manager should ensure that the team ground rules are consistent with the project vision and the agile principles and values. By defining the team ground rules and sharing the project vision, the project manager can help the agile team to understand the product owner's expectations, deliver value to the customer, and improve their performance. References: PMBOKGuide, 6th edition, pages 77-78, 541-542.