As far as your database server migration, it sounds like you’re on the right track. TNSName entry mods are essential ofcourse. Ensure that your destination tablespaces have similar storage capacities as your source so you won’t get import errors. Make sure you’ve got the same Oracle schema/users setup on your destination Oracle database server, and you should be good.
Also, in reference to your future intention of upgrading and/or migrating to 10G App Server, the Upgrade Assistant utility should prove to be helpful. Check it out.
This forum should be very helpful too:
An asktom webpage also has good material: