So I see a few problems with what you want, for a raid5 setup you will need at least four drives, since your information is striped against 3 and then the fourth is a parity drive. with 3 drives you have an incredibly high likelyhood of losing your parity drive.
To my knowledge, you will need to wipe the drives to put them in any kind of raid. Since striping is essentially making custom sections of blocks; I don't think mdadm is smart enough to also move data files as well.
I would really recommend holding off on your project till you can back up the information, and get a fourth drive. I know there is a lot of talks between raid5 and raid6, but for me I really prefer the peace of mind that raid6 gives.
Edit: seems like it is possible with at least raid 1:https://askubuntu.com/questions/1403691/how-can-i-create-mdadm-raid1-without-losing-data
What you want is gamefaqs.com. I've been using that site since 2000 to get guides for any game. All in html so you can print/download however you wish
I don't think metadata tracking would work with a p2p solution. Why would I want potentially terabytes of metadata for media I will never consume.
In my opinion, musicbrainz is already doing what you want with the big benefit of not being forced to store a full copy of it. If there is metadata missing from musicbrainz, then maybe you can help the community by trying to track it down and then add/update those values in the db.
It's even older than that, Sins originally came out in 2008.
I think this article is rather misleading, or the headline is specifically. Before this article was written there was DMC 3 Special Edition, DMC4, DMC 4 Special Edition, and DMC HD Collection.
DMC 3 Special Edition and DMC 4 are the two being removed. DMC 3 SE was a terrible port that barely runs on just about any machine, and DMC 4 is just the inferior version of DMC 4 SE.
DMC 3 is still available in the DMC HD Colleciton, and is actually playable. So Both games are still available in their actually playable form.