A supplier's catalogue is read in and kept current: products, variants, stock, prices in their currency. Orders go to the right supplier or warehouse; duties and shipping are worked out per market. Many suppliers, many countries, one store. The products you hold yourself go in the same catalogue: typed in, uploaded from a spreadsheet, or fed from a Google Sheet.
Suppliers get a portal of their own — their orders one parcel at a time, their monthly statements and the ledger behind them, their payouts on their terms — with their own sign-in and their own people, managed by them.