The first step that the business analyst should take to begin overhauling the Opportunity object is to understand the current business process. This is because understanding the current business process helps to establish a baseline for measuring the current state of performance, identify pain points and opportunities for improvement, and align with the desired business outcomes. The business analyst should use techniques such as interviews, observations, surveys, or process mapping to understand how users currently use Salesforce opportunities and what challenges or gaps they face. References:
https://trailhead.salesforce.com/content/learn/modules/salesforce-business-analyst-certification-prep/business-pro