Collapsing some fields in add content page
You could try the Field group module. You can set field group settings "collapsed" and deselect "Mark group for required fields". It collapsed the field group by default.


  Fieldgroup will, as the name implies, group fields together. All
  fieldable entities will have the possibility to add groups to wrap
  their fields together. Fieldgroup comes with default HTML wrappers
  like vertical tabs, horizontal tabs, accordions, fieldsets or div
  wrappers.