RAID 0 is the only type of RAID that increases performance, every drive you add to that is increasing the storage by that amount, the disadvantage to this is, if one goes you lose all your data. RAID 1 is backing up the drives. So there is a mirror of every drive. RAID 5 is at least 3 drives, with one of those as a backup drive. This is slower than having a single drive. These should all have drives of the same size.
The Armor and Kandalf have fans by the hdd bays. At the front is a 120mm sucking air in, and the hdd bay at the back has a 92mm fan sucking air out of the case.