you can mostly use the same commands you are using with TSM, if you say you are using -n 20 .... Just executed from command line it will trigger a 3rd party command line backup with your commcell (regardless, i think you need to create the client and DB instance in commvault).
When you perform an agent based backup from the commvault gui and afterwards check the output in the saparch folder, you will find that cv executes regular commands:
command_line brarchive -d util_file -OSC -cds -c -u /
There is no reason you can't match that command and run it directly, either as permanent log backup with -f or to limit it with -n.
All these options belong to brarchive and not commvault. But remember, when using the 3rd party integration with scheduling via UC4 you may miss some possibilities when it comes to automatic alerts from the commserve and i am not sure if all reports will work properly with 3rd party backups.