I'm not sure that this is going to fly. After 6 days and 27 posts nobody is any the wiser. A graphic will not be a specification.
The specification, should show what you want out of the system and include table structures. Table design is the beginning. Plus, you cannot proceed with a program segment. You must have it all. Otherwise you will be continually updating existing tables as you add new ones. Which will affect any existing code. You will be amending all the time, which is not the way to go.
If you cannot specify what you need, even experienced developers cannot help you. They will have a good idea what you want but not actually what your imagined detail. Then after you have the system working, you will need to install security to prevent tinkering. The list goes on and just from what you have written to date, my guess it will probably take an experienced developer with a stack of libraries maybe every day several months. For you to do it, I'd say at least 12 to 18 months to include learning and understanding for something the business can rely on.
You are using Xero which from a (very) brief look does not allow import/export and is quite basic. Your proposed system whilst maybe not needing to be integrated, will need to export to and possibly import from accounts. Otherwise you will need to manually post invoices. Which was pointless in 1985, never mind 2025. You will need to use a business accounting system. SAGE will be fine and some versions may do everything that you want. SAGE also have approved add-on systems. Xero is unlikely to suit an expanding business. Don't be tempted into using spreadsheets. This is a database application.
One thing that you can be assured of, is that what you want to do has been done before. Many times. There will be many systems out there but it
will take effort to find them and assess. From where you are I'd suggest you use your time running the business. Get reps in, give them your spec and see what they have. If that fails, then maybe start burning the midnight oil.