How do you use forms to populate content type fields?
You seem to be going in a slightly wrong direction with this (until I'm missing or not understanding something). If your goal is to create a node based on the data users send via a custom form then it can be done in the form submit handler. Fields added via the GUI don't need separate handling. For example if you are using node_save() then adding a custom field value could look similar to this:

$node-&gt;language = LANGUAGE_NONE; // Or e.g. 'en' if locale is enabled.
$node-&gt;field_name[$node-&gt;language][0]['value'] = $form_state['values']['name'];


and with drupal_form_submit():

$new_form_state['values']['field_name'][$node-&gt;language][0]['value'] = $form_state['values']['name'];


There's a solid amount of information available about this on the web that you might want to check out for further assistance (like this, this and this).