Hello
I can help you to create the Quarterly Grouped Summary Fields, as well as the Yearly Customer Grouped Summary Field, I have extensive experience with FileMaker Pro for over 25 years and after reading your project description, I have set up a test database and have now successfully set up the structure to create the exact requirements you are seeking.
I will use a method of relational grouping to create the necessary fields for you, which you can then display on your invoices, or elsewhere.
If you would like to send through a copy of your cloned (no records) database, I can update the structure for you and complete the project.
Thank you
Darren
Edit: Just a quick update, I have just completed another project and so have some time available now that I can complete your project for you, if you would like to get back to me and send through a copy of the database, we can get that updated for you.