Newbie here - several questions about failing DX4000

Some more info - the DX4000 is 4 years old (almost exactly a year out of warranty based on calling WD support).

I asked the tech’s opinion about getting the replacement drive (and likely the others will fail in the shorter term) vs. getting a whole new NAS. He said get the 1 drive (i mentioned I’d get their newer NAS, so it wasn’t like he’d think he was losing a sale).

I called their wd store and they are out of stock on the 2GB drives for this, suggested I look on line and he also said - get the drive rather than their mycloud nas.

I found this:

which leads to this:

I’m looking to install that setuprst.exe, but it wants .net 4.5.

if I do that install then I can just use some other 2TB SATA drive (yeah, something reliable because it’s doing raid 5). That idea of using the intel raid controller is still a viable answer?