alright so I have more info now.
Wow so you're having to do this without the help of your IT department? So strange.
well, i get "help" from them, they just don't have a solution for me and so it falls on me to figure it out, especially since i'm basically the only one using it. ::tears::. no one is a dedicated IT person here, anyway. (they have other roles they play in the company and we contract out a lot of the work for the IT stuff)
In your situation i think one of two options would work best.
1. Buy/Build a PC with enough 3.5'' bays that you think will be enough, if you can't build the PC i could probably help find a retail one with a decent amount of bays. Put Windows 10 (really, keep) on it and enable Storage Spaces. Setup storage spaces across all data drives with Parity enabled. Enable network sharing and create a network share to said Storage Space. An inexpensive Norco rack would be preferable (20 drive case for $300) but if you don't have access to the rack this isn't really an option.
2. Buy a large Synology NAS and use "Synology Hybrid RAID". An 8 Bay DS1815+ runs about $850. The 12 bay version runs about $1300.
Both these options would allow you to expand by 1 drive at a time, with different sized drives (these are the kickers). Both options would have some parity, and both options would be relatively inexpensive and better than what you are currently doing.
There are a couple caveats to any selection , let me know if either of these options sound good or if you are thinking of something else.
Ok, so with #1, do I need to have a "server" for it to work, or just a server rack? The stipulation with #1 is that we have a server that is going to be retired within the next couple years and is not being replaced.
I don't know if the server rack is staying, leaving, what have you. Can a Norco rack function without an actual server, over a network, and just function with the PC over the network?
When I brought up solution #1, basically my manager said it wasn't going to be a good idea since the server was going to be eliminated. He said its possible that we re-purpose it for storage purposes, but that maintaining it would be a cost in itself and made me not think it was a great idea long term after all if it is required. It basically leads me now to the conclusion that #2 is the only actual option.
With #2, do I still need to figure out an independent backup solution, or will the Synology Hybrid Raid (SHR) be appropriate enough to not have to worry about duplicating everything and storing it elsewhere, such as on external hard drives?
Seemingly I won't be able to consolidate my current storage (approx 34 TB by my last count) since we would then need to get a second NAS probably. I recently calculated our growth, and we add about 1 TB of video normally per month, plus whatever comes in otherwise randomly. If we end up filling up a 12-bay with 4 TB hard drives that should potentially last for a while before having to get another.