The first step to address the issue of complaints from business executives regarding the amount their units are being charged for IT services should be to quantify consumption and service level agreement (SLA) achievements per business unit. This will help the CIO to understand the actual usage and performance of IT services by each business unit, as well as to justify and communicate the chargeback rates based on the value and quality of IT services delivered. Quantifying consumption and SLA achievements can also help identify and address any inefficiencies, discrepancies, or gaps in IT service delivery or chargeback methods.
Agreeing to reduce charge rates and improve relationship management with the business, looking into outsourcing of support functions to drive down the cost structure, and asking the CFO about budget revisions for the business units' IT expenditures are possible steps to take after quantifying consumption and SLA achievements, but they are not the first step. Agreeing to reduce charge rates without understanding the underlying causes of the complaints may result in underfunding or underpricing of IT services, which may affect their quality and sustainability. Improving relationship management with the business is important, but it should be based on transparent and accurate information about IT service consumption and chargeback.
Looking into outsourcing of support functions may reduce the cost structure, but it may also introduce new risks and challenges for IT governance and management. Asking the CFO about budget revisions may help align IT expenditures with business priorities, but it may not address the root causes of the dissatisfaction with IT chargeback.
References := IT Chargeback Drives Efficiency - Uptime Institute Blog; What is IT governance? A formal way to align IT & business strategy; Chargeback vs. IT Governance - HEIT Management.

Enterprise architecture (EA) is the best option to support the planning of IT investments required for the enterprise, because EA is a practice and a discipline that describes and documents the current and future state of the enterprise's business processes, applications, data, infrastructure, and security, and how they align with the enterprise's vision, mission, goals, and objectives. EA can help the enterprise to plan IT investments by providing a holistic view of the enterprise's IT architecture, identifying the gaps, needs, and opportunities for improvement, innovation, or transformation, and prioritizing and selecting the IT projects, programs, and portfolios that deliver the most value to the stakeholders and customers. According to ISACA's CGEIT Domain 2: IT Resources1, "EA is a key enabler for IT investment planning and decision making. EA helps to ensure that IT investments are aligned with business strategy and support business outcomes." Furthermore, according to ISACA's article on EA2, "EA can help to optimize IT spending by reducing complexity, duplication, and waste, and by increasing efficiency, agility, and interoperability." Therefore, EA is the best way to support the planning of IT investments required for the enterprise.

Before adopting cloud services, it is critical to establish the organization's risk tolerance levels. This ensures that decisions regarding the use of cloud services align with the enterprise's ability and willingness to accept risk, such as data exposure or operational disruptions. Risk tolerance informs the creation of SLAs, third-party management frameworks, and BCPs, making it a foundational step. References: ISACA Cloud Computing Governance guidelines, CGEIT Exam Manual.

The first thing that should be done to reduce the complexity of the IT landscape is to conduct strategic planning with business units. Strategic planning is the process of defining the vision, mission, goals, and objectives of the enterprise and how they will be achieved. It also involves aligning the IT strategy with the business strategy and ensuring that they support each other. By conducting strategic planning with business units, the enterprise can identify and prioritize the IT needs and expectations of each business unit, as well as the commonalities and synergies among them. This can help to reduce the complexity of the IT landscape by eliminating duplicate technologies, resolving conflicting priorities, and creating a coherent and consistent IT architecture that meets the business requirements and delivers value. The other options are not as effective as conducting strategic planning with business units for reducing the complexity of the IT landscape. Promoting automation tools used by the business units may improve efficiency and productivity, but it does not address the underlying issues of duplication and conflict. Migrating all in-house systems to an external cloud environment may reduce costs and increase scalability, but it does not ensure alignment and integration of IT systems across business units. Standardizing technology architecture on common products may simplify IT operations and maintenance, but it does not consider the specific needs and preferences of each business unit.

A common risk management taxonomy is a set of terms and definitions that are used consistently across the enterprise to describe, measure, and report on risks. A common risk management taxonomy is essential for integrating IT risk with the ERM framework, as it enables a common understanding of risk concepts, categories, and levels among different stakeholders and functions. A common risk management taxonomy also facilitates the aggregation and comparison of risks across the enterprise, and supports the alignment of risk appetite and tolerance with business objectives12. References: 1: Integrated Enterprise IT Risk Management (ERM) Programs - CohnReznick3 2: Introducing Risk Taxonomy - ISACA4