When you want to convert a database created in the default characterset to a multibyte characterset, there were two basic approaches - the safe export/import and the not-for-the-faint-of-the-heart alter database convert internal. In either case you had to follow a string of activities - checking the presence of incompatible values by running csscan, etc.
There is a new tool from Oracle to make the process infinitesimally simpler - Migration Assistant for Unicode. It's a GUI tool that you can install on the client. A server side API (installed via a patch) does all the heavy lifting with the client GUI providing a great intuitive interface. You have the steps pretty much laid out for you. But the main strength of the tool is not that. There are two primary differentiators for the tool.
With these two differentiators in place, the tool has great future. Check out everything on this tool at http://www.oracle.com/technetwork/database/globalization/dmu/overview/index-330958.html or just visit the booth at #OOW Demogrounds in Moscone South.
Oh, did I mention that the tool is free?