There seems to be two types of homelabbers with regards to storage:
Those who take storage redundancy seriously
Those who don't seem to care
I've made the mistake of asking the second group what they thought about types and quantities of storage, and I got quite a few "why are you concerned?" type questions. My guess is that they regard obtaining data to be free/trivial, so storing it redundantly is a pointless cost. I'll just say that I don't share their cavalier attitude.
This setup is my personal goal, and I think refurbished drives are the best way to go about it (provided they are reasonably taken care of). If you're working in a redundant setup, the age of the drives matters a lot less.