Hi,
Is that your functional spec or technical spec?
Thru filed based we can't decide what data source/flow needed.
please sit with your business users or functional team, Get proper requirement.
Thru requirement itself you may think related data sources.
later check required fields are part data source ot nor.
Later think about look ups or enhancement as per the availability bw existing data if required fields are not part of standard data source.
As my guess you may FI/SD billing data source.
please look for them on google.
Thanks