Bacula: best practise for labeling and initial start

I'm currently starting with bacula for backup and have a few questions for best practices.

Current situation:

• I want to back up a slow changing max. 12TB (currently 8TB) dataset to a external LTO4 drive. Due to the small incremental changes I prefer the strategy to do a full backup every half a year and monthly incremental.
• The full backups should be done alternating to 2 pools so that one can be kept offsite
• I managed the config (see the bottom for relevant parts) and my testcases on disk base are looking good

So here are the questions:

• How can I tell bacula how many numeral digits should be used for autolabeling (default is 4)? As my prefix is 4 digits long and tapelabels (even if I currently don't need them) only support 6 digits, I want to force bacula to autolabel with 2 numerical digits (e.g. FS1T01 – 99) to keep consistency.
• Is it better practise to feed bacula the tapes on first backup run and let em do the labeling or to add them to the pool before running the job?

relevant config extracts:

Director:

Pool{
  Name = FullSet2
  Use Volume Once = yes
  Pool Type = Backup  
  LabelFormat = "FS2T"
  AutoPrune = yes
  VolumeRetention = 350 days
  Maximum Volumes = 15
  Recycle = yes
}

Pool{
  Name = FullSet1
  Use Volume Once = yes
  Pool Type = Backup  
  LabelFormat = "FS1T"
  AutoPrune = yes
  VolumeRetention = 350 days
  Maximum Volumes = 15
  Recycle = yes
}

Pool {
  Name = DiffSet
  Use Volume Once = yes
  Pool Type = Backup
  LabelFormat = "DS1T"
  AutoPrune = yes
  VolumeRetention = 1 day
  Maximum Volumes = 10
  Recycle = yes
}