Hdd Migration Advise

Migration advise/feedback needed…

I bought a DS923+ to replace my DS415+ (4x3Tb HDD @ 80% (7.1TB)) deciding not to buy new drives (yet) to spread cost. I did a HDD migration all going well but since realised I am using ext4 but want to move to btrfs. I currently have no backup source but have now ordered 3x 8TB HDD arriving this week.
My plan to upgrade the HDD in the DS923+ and move to btrfs is as follows:
1.Individually replace each HDD in the DS923+ repairing after each replacement until the DS923+ has all 3 new HDD leaving the old drives redundant.
2. Installing the old drives into the DS415+, setting up as btrfs in SHR
3. Backup the DS923+ to DS415+ with hyperbackup
4. Deleting DS923+ volume and creating new one as btrfs
5. Restore data from DS415+ using hyperbackup to DS923+
6. Use the DS415+ as an offsite backup

Obviously plan is to try an retain as many settings/packages as possible along with data, does this sound a logical process to follow?