Software RAID (mdadm) - Running RAID 0 alongside RAID 1

Draft - Incomplete, but kept mostly for my own sake so I can find my way back to it at a later date.
Specific scenario: Hetzner installimage with RAID1 or RAID10
RAID10 with less storage for the OS and "important" stuff.
Make sure to comment out the 
all option, that allocates the rest of the disks to say 
/home or similar.
RAID0 with the remaining storage across all 4 of the disks (Linux ISOs) that's easily replacable.
Create empty partitions using 
fdisk. Ended up with: 
/dev/sda5, 
/dev/sdb5 etc.
fdisk /dev/sda
n (new partition)
Note the partition number. For me the last partition number ended up being 
5 for all disks, which I used in the 
mdadm command later.
Select start block, end block etc. (or just leave default to use remaining space)
w to write partition table
Create a new RAID0 array using new partitions, with 
mdadm:
mdadm --create --verbose /dev/md3 --level=0 --raid-devices=4 /dev/sda5 /dev/sdb5 /dev/sdc5 /dev/sdd5
Note: Might wanna check 
lsblk to verify that 
/dev/md3 isn't already taken. When I ran 
installimage I ended up with:
md0 = swap
md1 = boot
md2 = root partition (
/)
Run 
mdadm --detail --scan and find the line that matches 
/dev/md3. Copy that line and put it at the end of 
/etc/mdadm/mdadm.conf
A lot of tutorials suggest piping that to 
tee -a /etc/mdadm/mdadm.conf so it appends all the lines to the end of 
/etc/mdadm/mdadm.conf. In this case since there's already an existing RAID array, there will be duplicate lines and potential for conflicts.
Double check that 
/etc/mdadm/mdadm.conf looks correct, then run 
update-initramfs -u so that the RAID array is available during the boot process.
TODO: Creating filesystem, mounting, append to fstab.