Yeah, pretty loud :P
70c is fine. No concerns there.
Yeah, that's a shame but it wasn't really a bother for the guy who got it.
Should be good!
Yes, so I think when you connect M2 drive it deactivates one of the sata port but you still have 5 available to connect to either SSDs or HDDs, so it shouldn't be an issue for you.
In addition to your poor cable management, your CPU cooler is overkill for the i5 8400...