Looking to add a large hdd or 2 HD’s raid1 in Windows10, looking at Plex, using a Vizio TV ethernet and the Vizio Plex App. I haven’t bought the TV yet or the hard drives. Looking for feedback on the best was to do this setup ?

Thx,
knight’

Thats some horsecrap, snooping and trakware has gotten out of hand, gee wizz!  What about using a Raspberry Pi 4 8GB/RAM to stream too for the TV,
 
https://www.adafruit.com/product/4296
 
Or just getting a wired Roku?

Hey, so I'm about to put together a completely separate streaming box for my Plex since I have 5-6 people streaming & multiple people at the same time brings my rig to its knees if I'm trying to game on it at the same time.
 
You honestly don't need RAID, unless you're really worried about data redundancy because you're constantly writing to these drives. I'm running a couple non-RAIDed WD Blue HDDs (7200RPM) and buffering usually takes less than 15-20 seconds before it starts playing. An extra 5-10 seconds when remote streaming from off my network.
 
What really matters for your build is that you're using a modern Wi-Fi router that can handle video streaming bitrates (or hard wired as you're stating you're going to do) and if your machine is going to need to transcode the videos to play on the Vizio TV (this will tax your CPU).
 
If you really want a smooth experience buy the Roku for smoother video as you won't rely on the crap hardware (and the reporting) built into the TV.

I run my plex on a seperate system.   I have media on my NAS and use an NSF share to connect to UNRAID as my OS.   You can put together a cheap system with a i7 3770 and above with quicksync and get some transcoding with 4-5 streams.   
 
Nice thing about UNRAID is that you can use the PC headless without a monitor and stick it in a corner and do all your server business on another PC through the IP address.   
 
As far as drives.  Plex media needs to be on a NAS type harddrive, since it will run all the time.  If that's what you desire.  WD red drives are good.   I have shucked a few WD Easystore drives.  You get more space for the buck.  Right now they are 199 for a 12 TB.  but best buy runs sales on the 8 TB for 139.  Those drives are basically NAS type drives.  Either wd red or white drives.   
 
so you can set up an old pc with windows, but it will need to have a monitor or UNRAID has a 30 day trial.   It's linux based, but has a gui.  Youtube is the best place to see what it does.   search for UNRAID and Plex server.   
 
now.  if you want real transcoding, look at a quadro P2000 or P2200.  that can get you 20 or so transcodes.   whereas nvidia based GTX cards are limited to two transcodes because they are locked.  You can unlock them with third party drivers if you wish.  
 
get a plex pass if you want hardware transcoding.  I got a lifetime for 75 dollars.  You can find sales from time to time.  That way I can transcode to any device I own if I'm away from the house. 
 
You don't have to have transcoding.   Just make sure all your media is in playable format for plex client.   that is only direct play.   

I use DVDFAB to trans code files that I download and covert to MKV (which Plex likes) using a EVGA 2080 Ti Ultra (DVDFAB uses the Cuda cores) and it went from 500 frames per second to (actually) over 2000 in some cases.
 
Average is about 1500 fps, usually more.

5400 or 7200 rpm hdds?  Most the content would be SD "less then 1080P"