Not sure if a RAID setup will work under OS/2, a hardware one might but then you're stuck if your MB dies unless you get another close to the same.
Even if it is a hardware RAID (highly unlikely), it might not work in OS/2. Some years ago, I got a SATA PCI adapter, so I could use SATA disks in my antique Asus P4VP-MX machine (I use that machine as an ArcaOS based NAS box, with a 2 TB drive). It has a hardware RAID on the card, but it is not usable with OS/2, simply because it needs a driver to turn RAID on at boot time. The whole RAID setup is done by code that is attached to the BIOS (no OS required), but it needs that driver to actually turn it on, or it just uses the basic, single drive, disk access (which is exactly what I want anyway). I did not bother to try to make RAID work <see below>.
At the time, I did some reading about how RAID actually works (there is more than one method), and quickly came to the conclusion that RAID is a rich man's toy, that isn't worth the work, or expense. Sure, if you are doing medical monitoring, or the machine isn't available for manual repair (like space craft), when storage goes bad, but in a normal work station it is nothing but unnecessary overhead. High performance, high demand, servers may justify it, but, as Arca Noae found out, if the RAID controller goes bad, it can take out ALL of the copies, leaving you to rebuild your system manually (you still need to make good backups, and that is less work than trying to manage a RAID). It is also a good idea to get a spare disk, because they all need to match, and a match may not be available when one goes bad (probably won't happen in the next 30 years anyway).
The rest looks like it should work, but you are probably spending more money than it will be worth. If you use the machine to run games, under windows, it might be worth it, but you are selecting a lot of expensive (even with discounts) hardware, that isn't going to do anything for OS/2 (the video adapter, for instance - most modern processors come with a video adapter built in, that will run circles around older devices, when using Panorama). Ask yourself: "what are you going to do with 1 TB of disk space?". Even 500 GB of disk space remains mostly empty, on my systems (except the 2 TB drive, which contains multiple backups of all of the rest of my systems).
Those large disks lead to a user not maintaining their disk space, which adds to the size of backups, and not being able to find what you are looking for. I know, for sure, that about 30% of the data on my HDDs should be removed (80%, if you count windows), but it is just too much work to do it. It would have been easy, if I had maintained a 250 GB disk, over the years. My two 1 TB drives are left with large empty spaces, just waiting for something to get lost on them. My most efficient system has a 30 GB disk, and 6 GB of that is taken up by win98 (I boot that about once per year, just because...). ArcaOS 5.0.6 is quite happy with the rest. Of course, I don't keep my photos, or music collection, on that disk. They get saved to a DVD (it does have a DVD drive - USB also works, but it is a single USB1 port), and that works just as well as having them on the HDD (I don't use that machine much anyway).
I did replace 500 GB HDDs, with 500 GB SSDs, on two of my laptops. That was not to gain speed (it helps), but more for shock protection. The price, of SSDs, is now in the "reasonable" range. If you want "high speed" disk, get a high performance NVME device, but be sure that it will use all 4 PCIe lanes for data transfer (4 lanes seems to be what is now available, it should be possible to use all 16 lanes, when/if the devices are produced).
