Hi Olivier,
Thanks for the feedback!
Just to provide some background on the three bullets:
The extracting tool will start complaining if you do not get all the fields that are part of the primary key of a table, therefore they are in the extracting part. However, we do not need them all in the app template on the way we use those tables.
You are right when it comes to the relation between payments and accounting documents. In the app template, the Accounting_document_ID uses what you mention. However, we use default the header - item relation between BKPF and BSE_CLR in the joins.
We use explicitly only purchase requisition = B. You are right, there is much more data in SAP available. That can be used by customizing this indeed.
Hopefully this provides some information about the choices at this moment. In general as you probably did for your instance, the app templates can be customized to support those asks. Thanks for sharing once more, we will take it into account in potential future improvements.
Thanks,
Kosmas