Can I create two volumes, RAID1 and RAID0 on two disk NAS326?

I currently have 2 disks in my NAS and RAID1 volume but running out of space. My idea is to have a RAID1 volume to keep the data that requires more protection and RAID0 for other data. I can't just do it from web-GUI, but I see a software RAID on my NAS, md0 for system, md1 for swap and md2 for data. So the idea is

* shrink ext4 on /dev/md2

* shrink md2 RAID1 using mdadm -G

* create fourth partition on each HDD (fdisk) and a RAID0 on them (mdadm).

* add a startup script to assemble and moint this RAID0 as /dev/md3.

Could anything be wrong with it, e.g. a configuration conflict or hard-coded requirement to have exactly 3 partitions on each internal storage will makes the device fail to find installed applications, etc?