Reddit mentions of Synology 4 bay NAS DiskStation DS418j (Diskless)

That is not an ideal set-up.

Okay, first lets talk server:

The NVIDIA Shield besides having the ability to function as a PLEX Server, it can also utilize the GPU for transcoding, so that should cover you and your parents just fine. Also, Kodi won't be necessary as Plex can DirectPlay almost all files on the SHIELD, even 4K files.

One thing you have to keep in mind about PLEX is the metadata file; my library (800 Movies, and 120 TV Shows | 30TB Storage Array) produces a MetaData file of 13GB, so a normal NVIDIA Shield won't cut it if you want to expand. You have the ability to expand the storage with a fast SD card, but I'm not sure if the ability to store the metadata in the SD card has been implemented yet (you have to check), in that case, the best alternative is the Shield Pro.

If you have a beefy computer you could also host the Plex Server on your computer, but that depends on you. The important thing is hard-wiring whatever you decide to go with through Ethernet for the best upload speeds.

Now as for the SDR-->HDR ordeal, it's true that a 4K file on a normal computer without tone-mapping will look washed out, but that depends on your set. For example, using PotPlayer and an extension, 4K HDR can be played on your computer (through the file itself) and it maps the colors correctly.

But like I said, it depends on your TV. One of my TVs plays 4K HDR movies just fine, and the colors look even better than my HDR set.., I don't know how it's converting the colors, but then again I don't have a $2,000 HDR TV to compare to.

Lastly, we'll talk storage and affordability. Storage is cheap, but paying half a thousand dollars for 8TB is a waste of money. The EasyStore 8TB External HDD at BestBuy occasionally drops down to $159.99-179.99 with the best deal being the 159.99. It's important you purchase the NESN model as those contain the $300 WD Red Drives with 256MB Cache, and meant for NAS 24/7 use. This is done through "shucking" the drive (you need a Philips and a Torx screw set) which involves placing hard card/gift cards at certain points to remove the drive from the enclosure and placing it either in your current computer, or a dedicated NAS machine.

So here are the following Scenarios:

1. PC Server SetUp+ Plex Client
   
   

• PC Plex Server (Faster, More streams/support, MetaData Storage)
  
• x3 8TB EasyStore ($480+tax) = 24 TB Storage
  
• Client(s): Nvidia Shield - $200 | Apple TV 4k - $105 | MiBox $69
  
  Only costs are Storage + Client
  
  

2. Plex Server/Client + PC Storage NAS
   
   

• SHIELD Server/Client (Low-Power, Can GPU transcode, always on | Need Pro model if you want to amass huge library)
  
• x3 8TB EasyStore ($480+tax) = 24 TB Storage
  
• Use PC to host HardDrives (but then it would be on all the time, so might as well host server on it)
  
  Pay for Drives+ Client/Server + NAS & Drives
  
  

3. Plex Client/Server + NAS Bays + HDDs
   
   If you want a small machine that's always on and consumes little power you can pair it with a NAS
   
   

• SHIELD Server/Client (Low-Power, Can GPU transcode, always on | Need Pro model if you want to amass huge library)
  
• Synology NAS w/4 Bays - Using this NAS with 1 EasyStore will place you within the price-range of the NAS you originally linked. The advantage here is that it will be more powerful and faster than the all-in-one 2-bay you linked. When you run out of space, you'll have 3 more bays that you can fill up with $160 WD 8TB Reds.
  
  Also, make a separate library for 4K files, and one for the 1080p/720P ones. Do a speed test on both your network and theirs; you need a good upload for high-quality files (4K files = 110 Mbps Upload bandwidth | 1080P Blu-Ray Remux = 40 Mbps upload bandwidth). They can transcode to lower bitrates fine, but this is just so you double-check everything.
  
  
  

What's the difference between these two hard drive bays which one is best for my use?

https://www.amazon.com/gp/product/B078YQHWYW/ref=ppx_yo_dt_b_asin_title_o00_s00?ie=UTF8&psc=1

https://www.amazon.com/gp/product/B074VB8DY7/ref=oh_aui_search_detailpage?ie=UTF8&th=1

My biggest concern with buying something that's 7 years old would be that it could die any minute and you don't have any warranty at all.

In terms of power, it'd probably do fine.

You can also buy a new DS418j for CA$390, but I don't know if I'd recommend that as it uses a Realtek RTD1293 CPU (Dual core 1.4GHz ARM), meaning you won't be able to run Docker and lots of other stuff.

If I were you, I'd hold out just a little longer and buy a new DS418 for CA$545 or something instead.

Synology 4 bay NAS DiskStation DS418j (Diskless) https://www.amazon.com/dp/B074VB8DY7/ref=cm_sw_r_cp_apa_i_uSJzCbKE17S3C

I was looking at this one, but it seems to be designed with surveillance cameras in mind. I'm on the fence about it because of that.

that exact model is on sale right now on amazon for $240

https://www.amazon.com/Synology-DS418j-4bay-NAS-DiskStation/dp/B074VB8DY7

I would suggest a ShieldTV, either the 2017 model or the 2019 Pro model, whichever is cheapest, for the Plex server. It supports hardware encoding in Plex and is also a top-notch streaming box. That'll run you $200 or so.

Then I would buy the cheapest 4-bay Synology NAS available, the DS418j, for $290, and fill it with 8TB drives. Ideally WD USB3 external drives which you can shuck to save money. They're frequently on sale for $130 or so apiece. This will give you 24TB of redundant storage so if a drive dies you won't lose any data.

That should come out very close to $1k, but if you have some money left over after that you can spend it on hats. Lots of hats.

https://www.amazon.com/Synology-bay-DiskStation-DS418j-Diskless/dp/B074VB8DY7