Particularly I don't like having to update my product bullet point features with each line item, it would be updated per group and spread to the individual SKUs.
In both Access and in FileMaker you would use two tables linked in a relationship for this. One table has one record for each group and the second stores related records with one record for each SKU. Updating data common to all records in a group would be a case of updating a single record in the groups table.
What approach would be used to still see the items un-grouped in a spreadsheet format, but also combined into a single page format?
And what data would you put and in what format on that single page? FileMaker can switch from list to table to form view all while on the same layout so your "spreadsheet" might be a list or table view and your "single page" view might be a form view. You might use one layout or two for this purpose.
You might also find that a summary report using sub summary layout parts a useful way to display such data: Creating Filemaker Pro summary reports--Tutorial
I guess really what I am looking for is some guidance on how to tackle this type of project with the attached flow chart.
But since you are working with a relational database, not a programming language, an entity relationship diagram may be more useful a way to plan the design of your database.