So I want to get an external enclosure for 3 or more hard drives. I want the option to have each run independently, or in a RAID setup. Is there something like this on the market?
You didn't mention a budget, money is always a factor. For 3 drives do a RAID5, don't be on the fence about whether to RAID or not as this is the kind of decision to make now and leave it that way, especially because performance in different configs will vary.