The attached screenshot shows that swap is not existent, thus the top displayed error. Using the Disk Wizard avoids that.
Replying to the subject "Can I use this to RAID 0 my 2TB + 3TB HDD?":
No, you can't convert your existing "standard" filesystem with your existing data on your existing disk to a RAID0. You can create a *new* RAID0 with the 2TB and 3TB disks, but your data on the 2TB disk will be lost.
Notice also that using RAID0 provides no redundancy, if one disk fails all your data will be lost.