S/4 On-Premise Interface to 3rd party Systems

Dear Peers,

ODATA and SOAP API which can be used for Connecting S/4 to 3rd party system. I have few basic questions please.

1) Can I connect multiple legacy systems to S/4 as to bring there respective PO/GR data in to S/4 System ? as client has many legacy to manage and create PO/GR currently which they would retain in future and so we need to Interface between all of them to S/4 Now.

2) Can all this different Inbound and outbound systems be seamlessly be connected with both OData and SOAP API connectivity? as i see few OData API cater our need and some time it is SOAP which could do the JOB, so can we have both accordingly as required.

Thanks for going through my long query and giving a thought on it...