FAL fields require complicated configuration. To make that easier, there is a function returning the TCA config for such a field.
Its usage for a field that allows only one file looks like this:
'dokument' => array(
'label' => 'LLL:EXT:publikationen/Resources/Private/Language/locallang_db.xlf:tx_publikationen_domain_model_publikation.dokument',
'exclude' => 0,
'config' => \TYPO3\CMS\Core\Utility\ExtensionManagementUtility::getFileFieldTCAConfig(
'dokument',
array(
'maxitems' => 1,
'minitems' => 1,
'appearance' => array(
'enabledControls' => array(
'dragdrop' => FALSE,
'localize' => FALSE,
),
),
)
),
),
A look into the source code of that function makes me not want to do that manually.