Form.submit(type, legacyMethod, skipPostSubmit, validateItem, sendEmail, backgroundSave)
but am unsure what type of field I should be using validateItem to get the function to validate the whole form
Any help would be great.
The code will validate the entire form if validateitem is not provided, or you could pass undefined or false.
That's correct, the validated item defaults to the root view item of the whole form if it's not provided (i.e. undefined, null, false, empty string or any other "falsey" value). If you want to be explicit you can specify the root view item with "Form.view".