Question Old power edge server as a NAS for Plex?

I've been idly looking to upgrade my NAS. I currently have a as-cheap-as-I-could-manage WD EX4 that can't handle Plex and hiccups just streaming video. It's getting full and the upgrade path isn't as clean as I would like. It appears to have a hard time when you replace all the drives in succession IE replace a single drive, rebuild and repeat with all 4 drives. Should be straight forward but I've seen a lot of posts where it struggles to do even that.

I have been considering going with a home built system. Maybe a Ryzen based system with a GPU for HW acceleration. I was looking for cases and noticed there seemed to be some pretty killer deals on old servers. Especially when you consider the price of the cases new on their own. But server gear is not my wheelhouse. I'm not entirely sure what I'm looking at beyond, rack mount case with two (2) CPUs, 32GB ram, redundant PSUs, and 8 drive bays plus low pro 5.25". That seems like a lot of system when considering a similar 8 bay NAS would have a wimpy Celeron, ARM, or Atom processor, a 2-4g of ram, and cost just as much or more. An 8bay diskless synology starts around $1000

https://www.amazon.com/PowerEdge-Se...dge+R720&qid=1584667997&s=electronics&sr=1-12

For reference a similar case is sold new for about the same price.

https://www.amazon.com/SilverStone-...9842EJX5RYP&psc=1&refRID=NYW6YNMXC9842EJX5RYP

Am I stupid for considering this thing? Are there restrictions on the drives? Can I get consumer sata drives and use them on this thing or do I need to get SAS drives? Can I load a FreeNAS, some other Linux distro, or a windows OS to run Plex? Or will I be stuck with the pre-loaded VMware due to drivers or licensing issues? What questions should I be asking that I don't know to ask?

Like I said this is not my wheelhouse. I know I can do a killer system using parts I'm more comfortable with. Could I get a better deal by going outside my comfort zone? I don't mind putting some effort into getting this system set up and running. But once it's running I would hope it's forgettable. IE I don't have to mess with it much. Or is server hardware more finicky if not running as intended?

For the moment I'm ignoring drive costs. However, if special server drives are stupid expensive let me know. I was just planning to use WD red drives. 4x in raid 5 to start.

Let me know if this is a good-job-gold-star idea or if I'm eating crayons.