Medium-sized trading company seeks invoicing program or small merchandise management system

We are a trading company and are looking for an invoicing program or small merchandise management system.

The software should have the following functions:

• Customer management: multiple contact persons per customer, possibly history of customer contacts (meeting notes). The customer master data should allow for individual fields and enable comprehensive evaluations.
• Different delivery addresses for customers
• Calendar, appointment management
• Invoicing: Writing invoices to customers, creating credit notes, etc.
• Article master data: Purchase and sales prices (small calculations)
• Small warehouse management (inventory list for storing a few items)
• Direct debits: Direct debits for customer invoices should be able to be sent directly from the program to the bank (HBCI interface or similar).
• Monitor open customer items
• Multi-client capability

Note: It would be ideal if we could also map the ordering process. I have not yet found a program that allows an order to be transferred to an invoice, because an order placed is charged to the customer on a one-to-one basis. Transfer was only possible at the purchasing or sales level, but not across levels.

Currently, approximately four workstations are planned. There will probably not be more than ten.