I have one of these mini PCs arriving soon. A little more money than I wanted to spend and no idea if this brand is any good. But it checks a lot of boxes for a backup server project I'm working on - eMMC for boot, microsd slot, M.2 2280 NVME socket, and a 2.5" SATA connection. They have some other variants as well that don't cost as much.
https://www.amazon.com/dp/B0B6P4MDWN
I originally got a used Dell Optiplex Micro from eBay for this. They come with a 2.5" SATA connection. But I learned the hard way that not all models come with M.2.
I don't think those characterstics are really worth considering when buying switches. For one, you're going to miss out on a ton of options if you restrict yourself to only switches that advertise those features. More importantly, with how mechanical keyboards are constructed, it's highly unlikely the board itself is waterproof. So, what good are waterproof switches when the board itself will fry when you spill your soda on it. I also think dust protection is another thing that isn't going to give any tangible benefit unless maybe you're typing in the open desert or something.