A missing file from the ctrnand could result in a black screen (i’ve had that happen myself). Go to 3ds.hacks.guide and follow their region changing tutorial (if there is a file missing, this should fix that)
Video guides are often inaccurate and outdated. Try using safe mode to update the system. (this can be done by holding down L + R + D-Pad Up + A, and then powering on the system.
Technically, cryptocurrencies aren't illegal, as long as you don't use it for criminal activity. If you sign up with an exchange, and that they get a tip from law enforcement, they have the right to freeze your assets.