1) You'll be gimped by the slowest drive. 5x super fast drives + 1x slow drive will give you the same resultant speed as 6x slow drives.
2) RAID 0+1 or 1+0 you'd need an even number of drives of at least four. You could probably software RAID 1 it with the existing array but it's likely beyond the capabilities of the onboard 'controller'. That and the fact you'd even further be limiting your array speed to your single 3 TB drive.
You could set this array up for fun but I wouldn't waste my time for anything other than a learning exercise.
2) RAID 0+1 or 1+0 you'd need an even number of drives of at least four. You could probably software RAID 1 it with the existing array but it's likely beyond the capabilities of the onboard 'controller'. That and the fact you'd even further be limiting your array speed to your single 3 TB drive.
You could set this array up for fun but I wouldn't waste my time for anything other than a learning exercise.