Do you have a CPU natively supported by your motherboard? If not, there is a high likelyhood you'll need to borrow one to update BIOS if it doesn't have bios flash with no CPU capabilities.
What's up with the 2 SSDs?
Fractal torrent is a nice case, if it comes with fans you do not need to spend 40 dollars on noctua fans. You can if you want to but I don't think it's that worth it.
The idea is sound-ish, but these drives are pretty reliable in general, and they are very fast. If you can afford them I don't see why not go with 2 of them for more storage but my comment was more about buying 2 different models. You could buy 2 of the cheaper drive for the same result.
It's not a wrong thing to do, but why waste your precious M.2 slots? Most normal boards have 2-3 M.2 slots. Having a spare of them would be great to easily expand storage without having to muck around with a 2.5" SATA drive
Fair enough but why 2 models? Why no simply buy 2 of the cheap one, it's not like it's gonna make a difference anyway (as a reminder, the steam deck can load games from an SD cart fast)