S/4HANA uses business partners for supplier and customer master data. One partner can have more than one role, but a supplier role doesn't make the same record a customer. The financial role and the process role cover different parts of the work. Supplier roles FLVN00 and FLVN01 support financial accounting and purchasing; customer roles FLCU00 and FLCU01 support accounting and sales.
Names can repeat. Use the partner key when you create or display a document, and check whether the record is blocked. Payment terms belong to the master-data context too. In these exercises you maintain original fictional partners and inspect the result. You don't need to create an invoice to prove the partner was saved correctly.