What is needed for an raid expansion enclosure?

[TheGreySpectre]

So I just filled the last hard drive slots in my case, so now any expansion needs to be external. I'm not really sure all the components I need to have a second case of drives. Some of them are obvious, I know I need a SAS expander, I know I need a power supply, I know I need an actual case and I know I need hard drives. What else do I need? Do I need a full motherboard and ram and stuff?

I'm currently operating a 12 disk raid 6 using an Areca 1880ix-12 card.