I have set Units and Increments (in Preferences) to inches but every time I try and create a new document it's defaulting back to picas
Maybe your File/Document Set up is set to Web or Digital Publishing?
Set the preferences with no files open - they will become the defaults for all new documents.
I have chosen "Print" chosen in "Intent"; I have tried changing from Custom to Default. I have been using this product through many versions and changing the setting in Preferences has always done the trick, but not on this version (which I recently upgraded to)