Go to your Google account settings and make sure that web & app activity, location history and ad personalisation are turned off.
Then uninstall/disable the Google apps you won't need then replace them with alternatives from F-droid (add the Izzyondroid repo too) like Cromite (in FFUpdater), Comaps, Thunderbird and QUIK SMS.
You should also follow standard practices like setting a non-easy to guess PIN code and also installing security updates.