backups for Oracle. what mode was db created in?

Regarding backups,

1. If a database was created with archivelog mode off, can we turn it on at a certain point in time to enable better recovery?
2. What is the best way to create a few extra control files for backup/recovery sake? We are using only one for one instance, and two for another instance. The two are in the same directory on the same disk. I assume ones on different disks are best.
3. I looked in the following tables to find out what database files are critical. How can I be sure of the init****.ora file being used? I assume that this file also should be backed up. select name from v$datafile select member from v$logfile select name from v$controlfile