Transfer of Purchase Requisition from ECC to other party through XI/PI

Dear Gurus,

I suppose to make one integration scenario in SAP PI 7.0. The scenario is that after releasing the PR, the data of PR will be send automatically to other party through a web service. I am relatively new to PI. I have few questions regarding this. Kindly help in this regards.

1) What would be the ideal scenario for this integration. I mean IDOC to SOAP, RFC to SOAP etc?

2) When the PR is released in ECC, how will i push it to SAP XI/PI? Will i use IDOC or what to push it to XI/PI?

3) How will i know that PR has arrived in XI/PI?

4) what configuration do we require in PI for this integration?

Kindly give your value able advise for this integration.

Thanks

Regards