In v1.5.2 can specify the size of a custom text field.
However, cannot specify a maxlength to stop user entering more the X characters.
Could the custom fields screen be changed please to include a Max Length parameter and the code in the hikashopText field class changed to something like:
$size = empty($field->field_options['size']) ? '' : 'size="'.intval($field->field_options['size']).'"';
$size .= empty($field->field_options['maxlength']) ? '' : ' maxlength="'.intval($field->field_options['maxlength']).'"';