Enable External Sharing Model to create external organization-wide defaults. This allows you to set different sharing settings for internal and external users based on profiles or roles. You can also use criteria-based sharing rules to grant access to records based on field values1.
https://architect.salesforce.com/diagrams/template-gallery/automotive-dealer-solution-architecture

Option A would involve using Salesforce Billing, which is a product that automates billing processes such as generating invoices, collecting payments, and managing revenue recognition. Salesforce Billing can also handle subscription billing scenarios such as renewals, amendments, cancellations, and prorations. Salesforce Billing can integrate with Salesforce CPQ to create seamless quote-to-cash workflows.
Option D would involve using Salesforce CPQ (Configure Price Quote), which is a product that helps sales teams create accurate and consistent quotes for complex products and services. Salesforce CPQ can also manage subscriptions by creating recurring quotes with flexible pricing models and contract terms. Salesforce CPQ can integrate with Salesforce Billing to create seamless quote-to-cash workflows.
https://trailhead.salesforce.com/credentials/b2bsolutionarchitect

there are two possible approaches for Salesforce org strategy: single-org and multi-org. Each approach has its pros and cons depending on the business needs, technology capabilities, governance policies, and operational requirements of the organization.
The best recommendation for the CIO is to prioritize completing an in-depth org strategy analysis, focused on the Business, Technology, Governance, and Operations requirements at SharpField. This should include an assessment of the newly acquired company and any other acquisitions that SharpField is considering. Additionally, the Solution Architect should recommend a single-org strategy and the development of strict processes for all acquired companies to follow. This will ensure that the Salesforce environment is organized, integrated, and secure. Finally, the Solution Architect should recommend the development of required integration layers to move the required shared data between instances of any and all acquired Salesforce instances.
https://www.salesforce.org/blog/develop-a-salesforce-org-strategy-to-achieve-a-unified-experience/

A system of record (SOR) is a source of truth for a specific type of data that needs to be accurate and consistent across different systems1. A system of engagement (SOE) is a platform that enables interactions and communications with customers and other stakeholders1.
Salesforce is a system of engagement for opportunities because it allows sales reps to create, track, and manage sales deals with customers23. Salesforce is also a system of record for orders because it stores order data that can be synced with other systems like ERP3.

it leverages the existing product and pricing data that is mastered in B2B Commerce and integrates it into CPQ via REST API, which is a standard and flexible way of exchanging data between different systems. There are connectors available on AppExchange that can help synchronize product and pricing data between B2B Commerce and CPQ, as well as streamline channel experiences and align order history. Integrating the final orders to the ERP via SOAP API can also ensure that the fulfillment process is consistent and accurate.
https://appexchange.salesforce.com/appxListingDetail?listingId=a0N3u00000MSk6gEAD