Key performance indicators (KPIs) are metrics that provide information about the achievement of specific goals or objectives.
Prior to selecting KPIs, it is most important to ensure that measurement objectives are defined. This means that the desired outcomes and targets of the goals or objectives are clearly stated and aligned with the organization’s strategy and vision.
Defining measurement objectives helps to select the most relevant and meaningful KPIs that can accurately reflect the progress and performance of the goals or objectives. It also helps to establish the criteria and standards for evaluating and reporting the results and outcomes of the KPIs.
The other options are not the most important things to ensure prior to selecting KPIs. They are either secondary or not essential for KPIs.
The references for this answer are:
Risk IT Framework, page 16
Information Technology & Security, page 10
Risk Scenarios Starter Pack, page 8