The "raid10" switch requires minimum of 4 drives according to https://btrfs.wiki.kernel.org/index.php/Using_Btrfs_with_Multiple_Devices#Creating_a_Multi-device_FS
. . . but I wonder if you might be able to use md-raid? or even if putting btrFS atop LVM might "trick" btrFS into thinking "bumbling fool" has 4 physical-devices? OTOH, would LVM or md-raid slow btrFS and what would be the point given that ext4 has online-fsck and is roughly as fast as btrFS in a "basket" of wide-ranging benchmarks for general-purpose use (i.e. unless you use your filesystem for a narrow range of tasks in which btrFS is faster than ext4)?
"sudo mkfs.btrfs raid[n]" also cannot yet give one subvolume a different RAID level than other subvolumes according to https://btrfs.wiki.kernel.org/index.php/Project_ideas#Online_raid_config ...but I'm not sure if that means the usage by "bumbling fool" of a hard-partition (for /boot & root) would suddenly make his /boot and root become "not a subvolume" and thus can be a different "mkfs.btrfs raid-level" WHILST ALSO RECOGNIZING & ACCESSING HIS /HOME PARTITIONS?
The problem I see with btrFS lacking this ability to have one large partition per physical-device, then making different raid-levels WITHIN that one partition, is you might as well use ext4 on LVM -- because the main difference of btrFS vs. LVM is that btrFS doesn't have PRE-DEFINED SIZES of /boot (or root) compared to /home, and in contrast LVM might need a LV resized (or deleted) in order to adjust its size relative to other partitions. btrFS loses that advantage --and ext4 has advantages that btrFS hasn't implemented yet, like the online-fsck-- once you strive for differing raid-levels (even if it works to put root & /boot on a separate hard-partition as "bumbling fool" did); also for dm-crypt/LUKS, you might as well use ext4-on-LVM instead of btrFS placed on multiple hard-partitions -- to avoid needing separate passwords for the various hard-partitions.
Until btrFS gets that raid-for-each-subvolume feature I think it isn't ready for "bumbling fool" (or me, since I use dm-crypt & wanna avoid having 3 passwords for 3 hard-partitions on each drive). ...but e.g. if "bumbling fool" just used 4 hard-drives, would his "mkfs.btrfs raid10" idea have worked?