I setup BTRFS RAID1 on my NAS recently, here’s what I gathered on BTRFS RAID levels:

• RAID1 vs RAID10:
  • RAID10 theoretically offers better performance (stripping), but the BTRFS implementation isn’t well optimized so you don’t get that much of a performance boost compared to RAID1.
  • RAID1 may also waste less disk space when using disks of different sizes compared to RAID10, here’s a simulator to check: https://www.carfax.org.uk/btrfs-usage/ . In your case it doesn’t matter since all your disks are the same size.
• RAID5/6:
  • It’s not only the write-hole, scrubbing is also broken (huge read amplification make performance unusable on large file systems).
  • RAID5/6 is slower than everything else (not a BTRFS problem, it’s just parity calculations).
  • I believe the BTRFS developers are getting (relatively) closer to fixing RAID5/6 these days, but they still don’t recommend using it. Switching between BTRFS RAID modes can be done pretty easily later without creating a new filesystem, so you could always switch to it later once it’s fixed.

In your case, I’d probably use RAID1 or RAID10 for data, and RAID1c3 for metadata.

EDIT: just saw that you don’t care that much about losing the data. In that case you don’t need any fancy RAID thing, as someone else said just add all your disks in single mode (the default), way simpler and you don’t lose any disk space.