Well, actually, all I can recommend to you now is to organize it all through an order, where to create services with goods that have suppliers listed in the "Suppliers" tab.
Then add them to the order, and I can offer to make the action of sending a letter according to the specified template for the products of the process, which will send the products to the corresponding suppliers (an array of products will be available that can be displayed in a table) - the development of such an action will take 5 hours.
Well, then you already said that you will do everything manually.
Look, I see that you need to automate the business process completely from scratch - there are integrators (business consultants) for this. I recommend that you use their services if necessary
https://crm-onebox.com/ru/integrators/