should i bring in 20 million customers from EBS to RightNow?

Content

One of our client uses EBS field service, and we will be implementing RightNow as contact center. each time a case is marked as 'field service' it will be synced to EBS/FS module. Thre are 20 million customers.

1. am i correct in assuming tht , all these customers MUST be brought into RightNow?

2. or the best practice is to lookup and fetch the customer's data each time a case is created? (and that customer also gets created in ORN?)

3. if contact table is empty, each time a case gets created via email, a new contact will be created! 

What are the best practices to follow?