As for the “Compare”, this is currently a limitation of EmEditor. Since a split window can’t contain different files, the two comparing files can’t exist in the same split window. This is the design of EmEditor, and it is not easily changed in future versions.
The Parameter Information for the Projects plug-in appears as a Tooltip (small yellow popup) if the Symbol list is active and understands the current language. The Symbol list understands the PHP language.
PS. Please don’t hesitate to create a new topic for each question.