How can I display a form button on top of the form?
If you use $form['actions']['my_submit'] like this, then you will get the button inside $form['actions']. $form['actions'] weight would be considered with the weight of other fields. Try the following code. 

 $form['my_submit'] = array(
  '#type' =&gt; 'submit',
  '#value' =&gt; t('My custom action'),
  '#weight' =&gt; -1000,
  '#submit' =&gt; array('node_form_submit', 'my_custom_node_form_submit')
 );