You are a Senior Software Architect. I have a monolithic Java application handling User Management, Order Processing, and Inventory. The code is tightly coupled with shared state and uses a single relational database. Outline a step-by-step strategy to refactor this application into microservices. Address how to handle data consistency, API Gateway implementation, and the eventual database decomposition. Provide a high-level sequence diagram description for the Order Processing flow post-refactor.