Multi Resource SupportActivating Multi Resource Support for your workflow model means that a single workflow instance will be started when you select multiple resources. It should be activated for your workflow model.

I would suggest you to check ths following doc where you can see how to create a workflow, invoke it, and monitor it.Adobe Experience Manager Help | Using Adobe Experience Manager Workflows

A field that allows the user to enter path.PathField — Granite UI 1.0 documentation

Do you see anything relevant in dispatcher logs ?

I do not believe the server is available during an upgrade installation but during the routine maintenance e.g. workflow purge, DataStore Garbage Collection, ..etc Ideally you should not let any access. You can block access via dispatcher.

Are you referring to Coral Datepicker ? Could not see anything in the documentation.Documentation | CoralUI

In Author mode, anonymous access is disabled for most part.You can enable anonymous user in Apache sling authentication service.

Check the relevant document to ensure you are not missing anything:Target Integration with Experience Fragments

You may want to check this:Obtaining Page Information in JSON Format

I have done this update and did not see any issues.try invalidating cache and rebuild libraries:http://host:port/libs/granite/ui/content/dumplibs.rebuild.html