Keeping 365 days of logs should not be a problem. The only issue is if the log indexes get corrupted and need to be rebuilt, this can happen if Iguana crashes.
When Iguana is restarted it will need time to scan the logs and rebuild the indexes. As a rough guide, assuming we have 365 days of logs at 1MB per day (365 MB total) it should only take a few minutes to rebuild the indexes on a basic PC with a single disk drive. On a machine with a fast disks (RAID, SAN etc) it will be much quicker. The manual page Log Age and Logging Performance indicates that the indexes (metafiles) for 20GB of data were rebuilt in 15 minutes on a test machine.
So why do you need to keep logs for so long? Probably for legal reasons, so you may not need to track everything in the logs. This FAQ suggests some archiving alternatives, For legal reasons we need to record 7 years of messages, how can I do this?