Hi, the first part is pure setup. On the CUSTOMER integration table mapping set Synch. Only Coupled Records to Yes, then new Accounts stop creating customers in BC and only the ones you couple yourself will sync.
The rest needs an extension. There is no standard mapping from Account to a BC company contact, the Contact table is already used by the CONTACT mapping against Dataverse contacts, and the new mapping wizard doesn't offer a table that is already mapped.
Coupling one Account to two BC records is not a good practice, even if it goes in you then have two mappings writing to the same Account and you'll have sync errors later.
What usually works is leaving the prospect only in Sales, then coupling the customer manually at the moment it converts, so the Account and its history stay the same one.
Glad to help - follow up if anything is unclear.
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Regards,
Grigorios Mavrogeorgis
Business Central Consultant & AL Developer
Work: Gmsoft Limited
Blog: insidebusinesscentral
LinkedIn: linkedin.com/in/gregorymavrogeorgis