Build RMAN catalog

We have implemented RMAN backups for our database around 5 months back. Initially to make the environment simple we didnt opted for a recovery catalog database. Now we would like to implement the Recovery catalog for our database and have few things to get clarified before going forward.

1. Our present control_file_record_keep_time is set to 7 days. If i create a catalog now at max i'll be having only 7 days of information . What about the earlier information. Is there any way i can get that?
2. All our backups are taken to Tape (Tivoli). Presently we have many backups on tape and we haven't deleted them yet. If we want to delete those old copies we are unable to do so as the information about those backup sets is not available in RMAN ( control file). how can i delete those old stuff without affecting the consistency of the tape/recovery catalog in control file.
3. We are planning to use the below approach to build the new recovery catalog from scratch and resync it to have complete tape backup information. below is the strategy i would like to follow..
   (a) create a rcat database & register it with database
   (b) resync the catalog to have the present control file information
   dumped to catalog
   (c) restore the oldest possible controlfile from tape ( which will
   be around 20days old) and try to resync catalog from controlfile copy . ===> i'm not sure about the effects of this command. Will this just updates the old information to catalog and leave the new information as it is? this is what i'm expecting ? but not sure how exactly it behaves. Any inputs from anyone already tried would be really helpful.
   (d) repeat the above process maximum possible times to make sure
   that we have maximum possible information.
   (e) clean up all obsolete backupsets from tape , which would ideally
   delete old information as this should be present in catalog by now.

Please review my above plan and let me know if it is the right way or not.

Any comments would be realy helpful.

Thanks & Regards,
Ravi.M

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