wordpress step form - how to move values to next step?

I am building a simple step form (step1 -> step2 -> step3)

At the first page, I did like this.

 if( isset($_POST['step1']) ) {

                        include_once( get_template_directory() . '/includes/form2.php' );

                    } elseif( isset($_POST['step2']) ) {

                        include_once( get_template_directory() . '/includes/form3.php' );

                    } else {

                        include_once( get_template_directory() . '/includes/form1.php' );

                    }

Each form pass value like this.

<form name="mainform" id="mainform" class="form_step" action="" method="post">
<input type="submit" name="step1" id="step1" class="btn_orange" value="<?php _e( 'Continue &rsaquo;&rsaquo;', APP_TD ); ?>" />

on Step1, agreement page,
But on Step2, input form for title, content, tags (real input form page)
then it goes to a function to save values like this.
(after save values, I need to move Step3 with several values such as post_id which just saved and name, price

//*************************************************************************************//
if( 'POST' == $_SERVER['REQUEST_METHOD'] && !empty( $_POST['action'] )) {

    // Do some minor form validation to make sure there is content
    if (isset ($_POST['title'])) {
        $title =  $_POST['title'];
    } else {
        echo 'Please enter a title';
    }
    if (isset ($_POST['description'])) {
        $description = $_POST['description'];
    } else {
        echo 'Please enter the content';
    }
    $tags = $_POST['post_tags'];
    $step2 =  $_POST['step2'];

    // Add the content of the form to $post as an array
    $post = array(
        'post_title'    => $title,
        'post_content'  => $description,
        'post_category' => $_POST['cat'],  // Usable for custom taxonomies too
        'tags_input'    => $tags,
        'post_status'   => 'publish',           // Choose: publish, preview, future, etc.
        //'post_type'   => $_POST['post_type']  // Use a custom post type if you want to
        'post_type' => 'us_step'
    );
    wp_insert_post($post);  // Pass  the value of $post to WordPress the insert function
                            // http://codex.wordpress.org/Function_Reference/wp_insert_post
    //wp_redirect( home_url() );




    echo "ok=". $step1;
    echo "ok=". $step2;
    echo "ok";

    //wp_redirect( 'http://domain.com/' );
    //wp_redirect( 'http://domain.com/thanks-page/', 301 ); exit;
    $step2 =  $_POST['step2'];
        $name =  $_POST['name'];
        $price =  $_POST['price'];
        $post_id = $_POST['postid'];


    wp_redirect( 'http://domain.com/step-form/', 301, $step2='yes' ); 
    exit;



} // end IF

// Do the wp_insert_post action to insert it
do_action('wp_insert_post', 'wp_insert_post'); 

?>

I need to make it move to STEP 3 with $name, $price, $post_id But wp_redirect does seem to bring values (arguments) How can I fix it to move them to Step3?

By the way, How can I get the post ID after it gets saved on function?

Thanks,