Hello Ashutosh,
For the step 1, instead of using the file, you can use IDOC's.
Use Idoc WMMBID01 or WMMBID02 to receive the data from external system as Inbound idocs.
and process the inbound idoc using the process code WMMB or function module L_IDOC_INPUT_WMMBXY to create goods movement.
Refer to the below link for more details.
Goods Movements (SAP Library - IDoc Interface: EDI Application Scenarios (BC-SRV-EDI))
Regards,
TP