Resizing Redo Logs

I'm using Oracle 10gR2 (10.2.0.4.0) 64 bits.

I got many times oracle ORA-00494 error and the database went down but since 29th of july the database have not been killed.
The error message is below :

ORA-00494: mise en file d'attente [CF] d�tenue pendant trop longtemps ( (more than 900 seconds)) par inst 1, osid 176484
ORA-00028: votre session a �t� ferm�e

My database is used for datawarehouse of many terabytes.

Initially the redo log size was 500Mbytes and I've set it to 3Gbytes. The maximum log switch is after 5 minutes. I want log to be switched every 20 minutes or every 30 minutes.

To obtain the size of redo logs I've executed this query :

SQL> select OPTIMAL_LOGFILE_SIZE from v$instance_recovery;

OPTIMAL_LOGFILE_SIZE
--------------------
54763

53,5 Gbytes is it not very big as redo log size? What's the maximum size of redo log? To set very big redo log size what are the requirements? Which precautions should I take before? What are the risks? Are any other ways to change the log switch frequency?