I may be mistaken, but generally, the self-hosted commerce scale unit is primarily used for in-store scenarios, not for e-commerce. The preferred and most effective way to integrate any e-commerce platform with Dynamics 365 using headless commerce is to utilize the cloud commerce scale unit. This option is scalable based on transaction load and volume, and it offers high availability.
If your integration requires bidirectional real-time communication, it is best to choose the cloud scale unit for optimal performance.