IT service provider (in the process of being established) is seeking a commercial office solution (project-based)

I am looking for a commercial office solution for my IT service company, which is currently being established, for my office to process and handle projects with or via approximately 30 partners (external freelancers). I expect (at least in the initial phase) a volume of several hundred invoices per year. The software I am looking for does NOT need to include any functions for resource, personnel, or project planning.

The solution must meet the following requirements:

• Creation and management of customer orders and related service orders to external freelancers
• Time recording and credit note procedure (invoices) for freelancers
• Integrated invoicing (outgoing invoices)
• Management of incoming invoices
• Integration of payment flows, deadline monitoring incoming invoices
• Dunning
• Accounting or interface to accounting software (DATEV)
• Ideally, there would also be an integrated function for creating customer quotes (which are then transferred to order management) with a service catalog (text modules) that can also be used to create orders for freelancers to close the counter items.
• On-premises or cloud solution
• Standard software if possible

Two to four software workstations are planned. MS Windows systems will be used.