Create a new MCAE business unit, recreate the configuration, and link it to a full copy Sales Cloud sandbox. This way, users can test the lead nurturing with Engagement Studio, the forms on the website, and the lead management in Sales Cloud without affecting the production data or settings23.
The recommended approach for setting up an environment in which users can test the functionalities of Marketing Cloud Account Engagement would be to create a new Marketing Cloud Account Engagement business unit, synchronize the production unit and the training unit, and link it to a full copy Sales Cloud sandbox. This allows for a dedicated training environment that can be synchronized with the production environment to ensure that data and configurations are consistent between the two. Additionally, linking it to a full copy Sales Cloud sandbox enables end-to-end testing of the solution. (Reference: Salesforce Help - Create a Marketing Cloud Account, https://help.salesforce.com/s/articleView?id=sf.mc_create_account.htm&type=5)

Review the established and planned dataflows to understand where the systems of record sit and where data is transported to already. This is an important step to assess the current state of data integration and identify any gaps or challenges that might affect the reporting solution.
Identify key drivers and high-level data scope behind the need for a consolidated reporting. This is an essential step to understand the business requirements and expectations for the reporting solution, as well as the key metrics and KPIs that need to be measured and reported on.
Review the system landscape to identify other existing solutions for reporting and start to investigate high-level cost impacts (incl. licenses aspects) for the most viable. This is a useful step to explore the possible options for delivering a consolidated reporting solution, such as using existing tools or platforms, building a custom solution, or leveraging third-party solutions. It also helps to estimate the costs and benefits of each option.

Generate a new permission set that grants access to the Order object and assign it to the field service users1. This way, you can provide granular access to specific fields and records without changing their existing profile or license. This can also improve performance by avoiding unnecessary queries and calculations for sharing.
https://trailhead.salesforce.com/credentials/b2bsolutionarchitect

Data migration is the process of transferring data from one system to another1.
Data migration in Salesforce requires careful planning, preparation, and execution234.
Data migration best practices include setting up a data governance plan, focusing on data quality, creating templates, verifying proper transfer, and using appropriate tools2356.

System of Reference is more appropriate for this question. A system of reference provides data or services for other systems but does not store data itself2. A data warehouse can be seen as a system of reference because it provides data for analytics or reporting purposes, but it does not store the original data from other systems.