Interior designer seeks order processing, invoicing, and administration

I work in interior design, which means I design rooms from the floor to the light fixtures, ceilings, painting, carpentry, etc. I design everything in 3D drawings, then determine the quantities of surfaces or light fixtures, etc., then I may provide the customer with a cost estimate, and if the customer approves, I prepare a detailed quote (which can have up to 3,000 items). This involves purchasing services from tradespeople such as painters, electricians, carpenters, etc., whose quotes must be included in my quote. It also includes merchandise such as lights, chairs, tables, etc. When I receive the order, I take on the role of general contractor to coordinate the individual items.

These processes must be managed, including requesting quotes from manufacturers and tradespeople, placing orders, and issuing partial invoices, etc. There must be interfaces to DATEV, for example, a dunning system, etc., in short, everything that is part of good accounting preparation. It would be important for email communication to also run through the software so that emails are automatically assigned to orders. Ideally, an interface to my CAD software could also be set up, but this is not a requirement.

I am looking for simple and easy-to-use software for order processing, invoicing, and administration that will make my life a little easier.

A maximum of three software workstations are required.