[Django]-In Django is there a way to display choices as checkboxes?

In terms of the forms library, you would use the MultipleChoiceField field with a CheckboxSelectMultiple widget to do that. You could validate the number of choices which were made by writing a validation method for the field:

class MyForm(forms.Form):
    my_field = forms.MultipleChoiceField(choices=SOME_CHOICES, widget=forms.CheckboxSelectMultiple())

    def clean_my_field(self):
        if len(self.cleaned_data['my_field']) > 3:
            raise forms.ValidationError('Select no more than 3.')
        return self.cleaned_data['my_field']

To get this in the admin application, you’d need to customise a ModelForm and override the form used in the appropriate ModelAdmin.