Explain what you want, first.
First you talk about RAID1 then you talk about RAID0 and you also talk about having both. So what do you want? You have to choose between:
- 4 disks in RAID0
- 4 disks in RAID1 (often not supported)
- 4 disks in RAID 0+1 (striping & mirroring)
Any change to the RAID array would mean all data on it is destroyed. Keep this in mind. Also, make sure you have a FULL BACKUP of your data you do not wish to lose.
A RAID can never replace a backup.