Usage of RMAN would make your life more simple and feasible. The only thing that you have to make sure is that you have the RMAN repository on an entirely different server and keep that one also backedup. The use of RMAN would really help you at the time of recovery process and it would be more easier,
The different ways you could do the backups are using incremental level 0 to 2. For details you might want to refer the oracle backup and recovery strategies. Try doing level 0 once a month and then level 1 in twice a week and level 2 the rest of the time. There are pre written scripts available at $ORACLE_HOME/rdbms/case*.rcv files for how to create the scripts in rman.
Hope this would help you.
Life is a journey, not a destination!