We keep the IDB Backup for 7 Days and let it run two times per day in times where no or nearly no Backups are active.
The media.log on the CellServer tracks each used Tape and marks the ones with an IDB Backup with "OmniDB", so you can use that to find the needed Media.
Having a specific pool for IDB Backups with only a few Medias is also a good idea. Personally suggest to keep only one IDB Backup per Tape, in case one Tape goes bad you don't loose all of your Backups.
Another usefull thing is the obrindex.dat File that is generated with each IDB Backup. It contains all Settings required for a recovery, including the Slot Info for your last Backups.
Default it is located in db40/logfiles/rlog/ but you can create a secondary copy of it using RecoveryIndexDir-Variable in global File. I configured a Script that mails this file after each Backup so that I have it on hand in case anything goes south.