Hello Gaurav.
Though very commonly required by industries, we are yet to take this process into SAP. So I also await for experience based responses to your query.
- The answer to point1 seems to be Creation of PR (ME51N) with account assignment 'F', where you can assign the Refurbishment Order (or any other Order of your situation) then create PO (ME21N) and then create Service entry sheets (ML81N). While creating SES you can assign a different Order (child Orders) to each line items of the SES if it is your case.
- And the Point2 seems relevant to Subcontracting process.
These links may be helpful to you for having some concepts to design your full solution.
External Refurbishment process for Repairable Spares with Serial number Integration
(You are getting many useful links in Google with string 'External Refurbishment' )
Steps in Subcontracting Process
Recommend search previous discussions, because I remember this was done many times. Also wait for experience sharing responses here.
Good luck
KJogeswaraRao