The Product Category Subcategory field is a required field for all Amazon Schemas. Amazon is currently supplying templates which are modified to a new standard format where the category must be unique and consist of 3 levels.
The Amazon Vendor API connector is only available for certain schemas and countries, which are released progressively by Amazon. Therefore, it is important to consider some factors. Here you can know more about those.
The Amazon API Connector using Catalog Sources (AFS) allows you to publish catalog content to Amazon in an automated way. This avoids going through many of Vendor Central's self-service tools in order to add and update products.
Sales layer offers several ways to protect a field, avoiding unwanted modifications. Something to keep in mind when there is more than one user working on the same account.