RAID questions with ML I'm looking to build a NAS box and putting ML on it.

I currently have two drives that are configured as RAID one that I am pulling out of a NAS box. 

I have one drive that I'd like to add to the two already RAID drives, but I'm not sure if that's possible.

And is it even possible to have one drive with data on it and then create a RAID with another diver without it removing/formatting the data that is currently on the main drive?
My initial reaction from how you staged your question: building a NAS from the ground up is a complex set of interrelated dependencies in both hardware, software and connectivity. You might be better off purchasing a ready-made or self-contained NAS unit.

You need to ask what you expect from a NAS: lots of storage or redundancy. The two-drive RAID you mention could be configured a couple of ways, and you may not be able to read the volume without the original RAID controller from the NAS.

Your inquiry into starting with one drive then adding additional drives sounds like some JBOD (just a bunch of disks) setups. JBOD only offers los of storage, but no redundancy.

RAID and NAS can both be elements of a storage solution, but in and of themselves, the two acronyms can also spell HEADACHE.