Hi Sri,
1) You can create MM and OM for two operations and assign it to two actions in process integration scenario.
2) When you create process integration scenario then you need to create actions, actually with in the action we refer service interface operation. design perspective process integration scenario give you more graphical representation of the scenario and you can quickly create the directory objects based on process integration scenario.Performance wise both same there is no impact on performance.
Regards,
Praveen.