Raid1 only protects you from 1 drive failing. You still need to backup important files/data to other devices as raid cannot protect from viruses, user error (accidental file deletion), large scale failure (something that destroys the whole pc)...
I would suggest installing that extra 1tb drive into an external enclosure and though its not my favorite form of an "only backup copy", its better than no backup copy at all
Cheers!
ps - you should also install windows with only the boot drive installed. Have the sata controller in the proper mode though (raid). Once windows is installed you can install and configure the raid array.