there’s nothing difficult. use the answers field as you have it now, omitting all other fields /1/. For the data I’d just feed the form builder an empty array $this->createFormBuilder([]), so that will give you the answer via $form->getData()['answers']. the ID can either be manually inserted into the form (hence you know the full name and can extract it from the request object ($request->request->filter('id')) or use it as URL parameter in the form’s action (via $formBuilder->setAction(), $request->query->filter('id')).
1 - I usually omit buttons in the form component as their only purpose is to make the browser send the form and they don’t carry any information. this also makes the form processing compatible to AJAX.