As far as whether your existing code will be able to work depends on if your portlets are standard JSR-168 or JSR-286 portlets? If they are then you should work without any problem. But if they are using any JBoss Portal specific code, then you would obviously have to do some modifications.
Yes, you definitely should switch to GateIn for the simple reason that JBoss Portal is not going through any further development. There should be a reference guide and user guide. What else do you need?
Thanks! I guess some tutorials would be helpful if they have. But featurewise, Jboss Portal and GateIn are the same or not?