Hi Ritesh,
Yes its possible to extract data from SAP into FLAT file using ABAP programing and place the file in the FTP server so that you can access the file from FTP... You can take help of ABAP person.
iDOC or PI -- i'm not sure you can check with ABAP person who can help you on it...
Not sure if delta functionality works for all the table extracts ....
Post the same in ABAP forums to get some help what you are looking for.
Regards
KP