Advanced Module and Layout file.

Hi,
I'm really lost in how to render the content of an advanced module in my main layout ($vars['body'])

in:
/app/fuel/modules/partner/controllers/Partner.php

I got:

<?php
class Partner extends CI_Controller {

    var $partner_config;

    function __construct()
    {
        parent::__construct();

        $this->partner_config = $this->fuel->partner->config();
    }


    function index()
    {
        ddd('index');
    }

    /**
     * Submit a new Partner Entry
     * @return void
     */
    function submit()
    {

        $this->load->library(
            'form_builder',
            array(
                'id'=>'addPartner',
                'form_attrs' => array(
                    'method' => 'post',
                    'action' => '/partner/submit'
                ),
                'submit_value' => 'Neuen Eintrag hinzufügen',
                'textarea_rows' => '5',
                'textarea_cols' => '28',
                'render_format' => 'divs',
                'label_layout' => 'top'
            )
        );

        $fields = array(
            'name' => array(
                'label' => 'Full Name',
                'required' => true
            ),
            'comment' => array(
                'type' => 'text',
                'label' => 'Comment',
                'required' => true
            )
        );

        $this->form_builder->set_fields($fields);

        $vars = [
            'form' => $this->form_builder->render()
        ];
        // render `/app/fuel/modules/partner/views/submit.php`
        $vars['body'] = $this->load->module_view('partner', 'submit', $vars, true);

        // how to render the form in my main layout in /fuel/application/views/layouts/main.php ?


    }

}

I could do something like this the CI way: $output = $this->load->view('_layouts/main', $vars, TRUE); but what is the fuel way including all the vars/fields that I expect from my layout?

and second:

I use the fuel form_builder how can I utilize all the fuel validation etc. that's used in the backend, after I _POST the form here in the controller? I think about retrieving all DB Fields like I would in Partner_model->form_fields();

Thank you!