Export/Import utilities is the only option for you because you are switching between databases and platform.
Make sure to run catalog.sql, catproc.sql and utlrp.sql. If you are using replication then run utlrep.sql also.
Sys user grants given to other users are not exported so use some application to just export the grants or find a script that will generate all the grants given from sys schema. I have the script email me I will email you the script of sys (table and col level grants ) they are important but not discusses a lot in issues because very less people use exp/imp for migration unless it's different, i used it.
hope this helps