Webform: Hide the "add more" button
If you set the 
"Minimum amount of items" and 
"Number of empty items" to the same number the add more won't appear. 

Here is a screenshot



Here is the YAML source for basic multiple text field

textfield:
  '#type': textfield
  '#title': textfield
  '#multiple': 5
  '#multiple__min_items': '5'
  '#multiple__empty_items': '5'


Here is the YAML source for multiple custom composite

custom_composite:
  '#type': custom_composite
  '#title': custom_composite
  '#multiple': 5
  '#multiple__min_items': '5'
  '#multiple__empty_items': '5'
  '#multiple__sorting': false
  '#multiple__operations': false
  '#element':
    textfield:
      '#type': textfield
      '#title': textfield
    select:
      '#type': select
      '#options': days
      '#title': select