...but as I have currently no other requirements that would validate the purchase of advanced...
I suggest that you rethink that. I know that it's a major added cost, but I think that anyone of any experience level that is trying to develop or modify a FileMaker database should use Advanced to do so. Not only can the debugger and dataviewer save you many hours of frustration solving issues, they are great teaching tools for exploring how parts of a FileMaker database work. I routinely test new calculations by first entering in the data viewer as a "watch expression", for example.
And I don't really use the Database Design Report to Document my solutions. It's a useful tool for analyzing certain aspects of my design, but it's way to voluminous to really serve that well as documentation.
I usually include as much documentation as I can inside the database itself.
There is a comments box for every field when you examine their definitions in Manage | Database | Fields
You can include comments inside calculations by enclosing them in /* */ or by putting them to the right of //
You can and should (must) add comments to your scripts
You can add layout text to a layout to document specific details about that layout. In FileMaker 12+, you can put the text off the right hand edge of the layout. In older versions you can use conditional formatting to make the layout text disappear when in Browse mode.
You have comment boxes in your Relationship graph
And you should use descriptive table, field and table occurrence names so that you can look at a field 12 months later and know it's intended function.
You can also do a write up in Layout Text or a text field of your database and hide it on a layout the user can't access as notes to yourself or other developers about the design of your database.
If all else Fails, you can write things up in MS Word or a similar word processor to supply additional documentation.
better start saving up then or maybe help myself to a not so little christmas present.........