Consolidating EBS on One Instance

All,

We are attempting to take 2 ORacle R12 instances residing on separate servers and create a consolidated instance on a new 3rd server. The data for the two instances would reside in separate operating units and ledgers in the target instance. I have lots of questions i.e. :

Are there any utilities to do this or a part of it?

What is the best approach? Are there whitepapers on this? Old project plans?

How to avoid a duplication in oracle id's i.e. org_id, ledger_id, customer_id, vendor_id, value_set_id's etc. etc. I believe we need to "append" the data to the tables but need to avoid data duplication.