I'm on the verge of wiping the drive and doing my clean installation due to similar issues. I can't help wondering whether settings synced to/from Windows 8 to a Microsoft account aren't somehow contributing to these issues.
Mail tiles are 100% dead for me. I had one Hotmail, one Gmail, and one edu account set up for two days. Regardless of whether the app was set to show messages as they arrive or poll for new messages every X minutes, the app failed to notify me of a single e-mail. Retrieving new mail required switching to each account and hitting refresh manually. I look forward to the Mail developers redeeming themselves in a future update. Clearly they have plenty of feedback on the issues. Also just saw this. Them settings.
I think that there are many features that are appealing. I'm also irritated that many aspects are buggy - you've mentioned the Schrödinger's tiles. Unfortunately, I think this carries across many features within the apps themselves, Mail being something completely unusable for me due to its inability to automatically check mail, and due to my inability to configure the app so that it can send mail through our org's servers. I think Task View and the updated command prompt/Powershell programs are excellent.
If your image checksums are correct, then try burning at the slowest rate available for your drive. This can help reduce errors, especially on older (typically less reliable) burners, which tend to be among the first pieces of hardware to die from old age on any machine. Alternatively, you can try installing from a flash drive rather than an optical disc.
You could call them for assistance if you're in a rush to upgrade. Many people are experiencing activation issues, since the servers responsible for checking licenses are swamped with traffic. Activation, at least from the post-installation side can require many (dozens) of tries before the server can be reached. If your issue arises from this, then you could try to validate repeatedly until it works, or just hold off for a few days while things die down.
Looking into it - could be run through systemsettings.exe, but still digging through regedit at the moment. HKCU\Control Panel\Quick Actions\Pinned Regarding custom Quiet Hours: I haven't tested these settings myself (via gpedit.msc), but they look promising.
Edit. I found one way of doing this, but I'm not sure it is the best way. Someone else can probably easily improve on it. Ok. Fire up Onenote. File > Options > Save & Backup. Jot down the URL of the notebook. Open regedit, modify HKLM\Software\Microsoft\Windows\CurrentVersion\ActionCenter\Quick Actions\All\SystemSettings_Launcher_Quicknote Replace data in Uri (default is onenote-cmd://quicknote?onOpen=typing) with onenote:the URL that you pulled from Onenote, e.g. it should start with onenote:https://..... Restart the computer. Obviously if it doesn't work well and your computer starts exploding, swap the default Uri value back in.
Well, what have you tried so far? In Control Panel > System > Notifications & Actions, you can disable "Show app notifications". Then hit "Turn system icons on or off" and remove the Action Center. I suspect you can also use gpedit.msc > User Configuration > Administrative Templates > Start Menu and Taskbar > Notifications settings to make Quiet Hour last forever.