Ok I'm sold Would you recommend a make/model? Would I be able to use plex on certain models not running on a PC?
You would, but with one caveat: The lower-powered Synology devices (like my 216j) cannot transcode video. That means you'd have to convert your videos ahead of time to match the device you're playing them on, which is a huge, impractical pain in the neck. If you're planning on using one as a Plex server, definitely get one powerful enough to transcode HD video. Plex has published a list of the capabilities of different NAS devices
here.
I was leaning towards a 4 bay, possibly the Synology 416 play. I would like to keep the total package under $1000. Don't think I really need more than 4 TB at this time and could add more drives in the future?
The 416play probably isn't going to work for Plex, and as I'm looking through the list, a NAS powerful enough to transcode with Plex is going to be pretty expensive (definitely blowing your budget.)
On the other hand, if you use
Synology Video Station software, which has a companion DS Video app (for the Roku, iOS, Android, and others), the 416play will be more than adequate because the Synology software takes advantage of the dedicated video hardware in the "play" devices, while Plex does not.
Just using Amazon's prices, a DS416play is
$415, and you can stock it with a pair of
WD 4TB Red drives for $145 each, or maybe three
WD 3TB Red drives for $109 each.
Lots of options on storage, which you can play with a bit using
Synology's RAID Calculator. Spreading your data across three 3TB drives would give you 6TB of usable storage, and room to expand in the future. The nice thing about the Synology Hybrid Raid system is that you can swap in drives of larger capacities, and the RAID will rebuild and keep working. Some of the space won't be utilized until the drives are all the same larger capacity, but it's a heck of a lot more convenient than having to start from scratch when going to larger drives!
If you're planning to go larger in the near future, you might start with the two 4TB drives, and add another as money allows. Starting with two 4TB drives gives you 4TB of storage with redundancy. Adding a third one later on will bring the capacity up to 8TB. A fourth will get you to 12TB. Definitely play with that calculator and see what it'll do.
Hope that helps!