Hi,
It is again very specific to client and company. Normally the requirement gathering happens first and then we give the effort estimation in man days.
Requirement gathering is usually done by the person who has expertise in that particular domain or module so that he can decide the timelines accordingly.
Sometimes client have ready made report templates so based on that also we can streamline from which all modules these KPI data is going to come.
I can keep on writing in that context but i would suggest you to go through ASAP methodology in SAP this will give you complete insight.
Yes regarding currency conversion functional people will maintain it and same will be updated in tables.
Lot of documents on currency conversion is already available just search the same.
Hope it helps.
Regards,
AL