I recently built a new gaming computer and was thinking about turning the old machine into a media server/player to connect to the home theater equipment (via a Marantz receiver/pre-amp?). By memory, it's an Intel 7700k with 32GB RAM and GTX 1080 Ti. I believe it has 2x 1TB M.2 drives, but I would certainly look to add several large spinners into the cages I previously removed from the case. There's a large bookshelf and an entire china cabinet double stacked of DVDs, Blu-rays, and 4K Blu-rays of various TV shows and movies. Ideally, I'm looking for something that's as easy to use as ripping CDs via iTunes and creating playlists from songs. I'd also like the media server to act like Netflix in remembering where you left off watching something (switch from binging TV show A to watching movie B and then returning to A where you left off). Any suggestions or how-to resources? Any rule of thumb for how much storage it'd likely need? I don't have a clear count on the number of TV shows or movies on discs in the collection, but it'd be nice to estimate the cost of the needed hard drives before I dive in.
Alright, so here's the skinny on running plex. It's pretty easy on memory usage, your big limiting factors are going to be HD space and processor, though the latter isn't really a concern if you're the only one watching it (if you are, say, however, sharing your Plex server with 9 people and they like to transcode to a different resolution than what the files are, that can start chewing up processor more than you'd think). The other concern is upstream bandwidth. Every person who is streaming a 720p title across the internet will take up 3-5mbit of your upstream bandwidth, and 10-15mbit if it is 1080p. 4k you can count on 30mbit being eaten up. Naturally this isn't a concern if you only use it from within your own home.... but if you are ever going to try to watch on the road (or share it with friends) that can be an issue. Transcoding can make something stream at a lower resolution, saving bandwidth but it uses a lot more CPU cycles.
Currently I run Plex on an old Xeon X5675 (which, granted, is 24 core) and has 48 gigs of ram, but your machine sounds like it has more than enough (mine is not just running Plex, it's also running a half dozen different dedicated game servers, some video stream mixing, etc).
Installing the plex server software is effortless. I don't even feel the need to explain it at all. It literally has a wizard that steps you through everything. All the server management is actually done through the plex web app, so really it's fine for the server to be headless.
From there you build your libraries. Sure you can just have one big lump library with everything in it, but I prefer to break things out thusly:
1) Live action Movies
2) Live action TV shows
3) American Animated Movies
4) American Animated TV Shows
5) Anime Movies
6) Anime TV shows
7) Music
Plex has certain built-in configurations for libraries of Movies, shows, music, photos, and "other videos" that make things get catalogued easier.
You can assign a "library" to use any folder or drive or whatever, and multiple locations. For example, here's one of my libraries -
I've just got a bunch of USB drives plugged into my server. F used to be the drive for all my animated stuff (movies and shows, american and anime) but it started to get full, as did my "live action" drive. So I threw on another 4tb USB drive (which became H) and added folders for the various flavors of media, and then just added the appropriate folders to the appropriate libraries. So you can start small on storage and add as you need it, and you'll be fine. You don't need high performance drives to serve media, but it might not hurt to spring for the kind of drives that are used to being left on all the time.
As for media size, it depends on the encoding method and quality. H.264 is less processor intensive (less compression) but has larger file size than H.265, but I try to get H.265 wherever I can. But the vast majority of torrents are still H.264.
H.264 usually will get you:
~8 megs per minute at 480p
~20 megs per minute at 720p
~45 megs per minute at 1080p
~200 megs per minute at 4k.
H.265 will generally cut those numbers in half.
YMMV.
Plex does do things like remember where you left off and recommend the next thing in line from things you've already watched, but it will not rip your physical media for you. You'll need to rip and handbrake it yourself through other means. But honestly, even stuff I had on DVD already, it was way less effort to just torrent it. Just be sure you have a VPN or seedbox if you go that route.