1) I agreed don't use RAID unless there's a good reason. For "data protection" you can use a tool like Acronis True Image to backup the Windows drive on an automatic basis.
Also for RAID1 both drives need to be the same size (AFAIK) or at the very least you can only effectively use the amount of the smallest drive as the SAME DATA must be on both drives.
2) spare SSD is mostly useful for games unless you edit video or do some other task that benefits. The SSD also won't "spin up" with noise and delay if using HDD power options (I have auto shutdown after 20 minutes of no usage).
So you might use the SSD for files you frequently use, including a download folder, if the main drive is getting full. I have my large MUSIC COLLECTION on a...