What is the best practice on extending Business Partner in S/4HANA with table like data?

My requirement is to extend the business partner in S/4HANA with custom table data (not single fields) in S4HANA ON PREMISE. Goal is to add multiple classification data to a customer's sales area (0..n). Screenshot below is just a mock-up).

I am reading a lot of stuff, to make sure I do it the right way. Coming from a SAP CRM background and having worked with business partners in the past, I thought this would be pretty straight forward. Just find the alternative/replacement of Application Enhancement Tool (AET) (used in SAP CRM for such purposes) and go ahead. AET (see screenshot below) enables you to create new fields and, more importantly, whole tables that would extend the standard business partner model (UI, DB tables, BOL, BDocs) in SAP CRM.

Now, I am seeing a lot of different things on extensibility:

• Custom Fields, for obvious reasons, only adds single fields to a business context (nice blog Adding Field in standard Fiori apps of S/4HANA with Custom Fields and Logic from Masaaki Arai)
• Custom Business Objects is able to add tables (create complex data with root and child nodes, OData services, ...)
• BDT seems to be directed to single fields and extension of GUI transaction BP (two very nice blogs from Andi Mauersberger: SAP S/4HANA Business Partner Toolset (BDT) at Business Partner and SAP S/4HANA Business Partner Field Enhancement)

I think the best fit would be in-app extensibility Custom Business Objects. This comes really close to AET from SAP CRM. It creates custom tables and CDS views, offers creation of an OData service and custom logic for determination and validation. The only thing it does not do, is create an association to the standard business partner.

Field type 'Association to Business Object' only offers very few standard business objects in its value help (see screenshots below).

Is there a best practice on how to extend SAP business partner in S/4HANA with table like data? Maybe somebody had a similar requirement and can help me out where to start.

Best regards Sascha