To save me a lot of digging about, does anybody know where the 'Disable notifications' setting is stored for each user? I want to update it programmatically.
I assumed user_preferences but don't see anything likely looking in there.
If you don't want database sessions (and you probably shouldn't) then you can leave out that stuff. There's very little that is mandatory in config.php.
Open the Developer Tools in your browser. Recreate the error with the Javascript Console tab open and check for any red errors.
If you are familiar with the tools, you might also want to check the Network tab. Look for the interaction showing the error and open that. What does it say?