"Finder" is buggy after Sierra upgrade

Back up your Mac if you have not done so already. To learn how to do that please read https://www.apple.com/support/backup/. To learn how to use Time Machine read Use Time Machine to back up or restore your Mac. The reason for creating a backup is that the symptoms you describe could be indicative of an impending hard disk drive failure, so securing your data is a primary concern.

Then, shut down your Mac and restart it in "Safe Mode". To learn how to do that please read: Try safe mode if your Mac doesn't finish starting up. Compare how your Mac works in Safe Mode to how it has been.

Then, restart normally. If the same problem returns, please read the section If an issue doesn't happen in safe mode for Apple's recommended actions.

Finally, you can temporarily create a new User Account, and log in to that account to determine if the problem also exists when logged in to that Account. To learn how to do that read How to test an issue in another user account on your Mac. When you are finished troubleshooting, you can remove the temporary User Account by following these instructions: macOS Sierra: Delete a user or group. Before removing it, confirm you don't need any of the files you might have created in that Account.

Let me know what you determine.

FWIW, Selecting files in the Finder while in icon view using Shift + Arrow seems broken at the moment. I can't speak to the other Finder issues because I don't have them.

Power or other problems related to unexpected system sleep, shutdown, lights or fans call for an SMC reset. Be sure to read the procedure carefully and follow all the steps exactly as written, even if they seem inapplicable or trivial.