Looking into Plex ...what all do I need to know?

[SpaceBooger]

I use it on my main PC (FX 6600, GTX 980, 16 GB of ram) and I play games. The only time you would notice it running is if you are gaming while someone else is streaming at the same time.
I use plex and love it. Especially before I allowed the kids to browse Amazon and Netflix alone. It is an awesome program and if your streaming device is not hardwired I highly reccomend makeing sure the server setting is set to your internet upload speed to avoid stutters or other buffering issues.

[Xoth]

Keep in mind when setting up your FreeNAS that it is very memory hungry. I only have 6TB using ZFS and have 8GB of RAM. I think sticking with a ratio of 1GB RAM per 2TB of storage or better you'd be more than fine. Another thing to consider is the power connections and requirements for hard drives.

I ran Plex for a bit, but moved over to the more open-source Emby, which is a similar alternative if your'e into that. Otherwise they are very similar. Also, my Emby server resides on a VM on a different machine than the FreeNAS fwiw.

[Anapan]

By default Western Digital drives power down after a few minutes of inactivity, and that's a good thing IMO. Starting a video on an external USB3 drive that's gone into sleep function takes 8-12 seconds while the drive spins up to access the file. You can use WD Drive Utilities to disable this function, but even with active fan cooling I think it's better for a mechanical drive to sleep when inactive for long periods of time to save on unnecessary mechanical wear.

[Anapan]

I found this Stylish theme that fixes PLEX after that 2017 update that made everything in the web browser UI look bad.
Plex Polished 3.0