What Tony said... plus I would add the following commentary...
The new scheme you mentioned would be the better way to go...
Configure your Vault Stores to remove 'Safety Copies... 'After Backup' and...
configure your overall schedule so you Backup Exchange, then archive, then backup the archive data (as you mentioned.)
Doing it in this order (with safety copies) ensures that you have multiple copies of data before things are deleted and gives you more recovery options.
IMHO I would do all of this as 'Full' backups every night (if possible) to simply the restore process.
Also, make sure you are doing the 'backup the archive data' part properly... which should contain at the very very minimum... 3 things... EV databases in SQL, indexes and vault stores. All three should be backed up while the storage service is in read only mode.
You should also be backing up things like program files, MSMQ, registry/system state, PST Holding Temp, Shopping, etc.
Refer to the backup in the Admin Guide as Tony suggested for more info.