Add meta boxes with WordPress editor boxes in them to your home page.

home-page-meta-boxes.php

<?php

/**
 * Create the meta boxes for the home as long as it is the home page template that is currently
 * being used.
 *
 * https://wordpress.stackexchange.com/questions/82477/how-to-add-add-meta-box-to-specific-page-template
 * https://developer.wordpress.org/reference/hooks/add_meta_boxes/
 * https://developer.wordpress.org/reference/functions/get_post_meta/
 * https://developer.wordpress.org/reference/functions/add_meta_box/
 */
function THEMESLUG_register_home_page_meta_boxes() {
  global $post;
  if ( 'templates/template-home-page.php' == get_post_meta( $post->ID, '_wp_page_template', true ) ) {
    add_meta_box( 'THEMESLUG-home-page-box-1-meta-box-id', __( 'Home Page Box 1', 'THEMESLUG_text_domain' ), 'THEMESLUG_home_page_box_1_meta_box_callback' );
    add_meta_box( 'THEMESLUG-home-page-box-2-meta-box-id', __( 'Home Page Box 2', 'THEMESLUG_text_domain' ), 'THEMESLUG_home_page_box_2_meta_box_callback' );
    add_meta_box( 'THEMESLUG-home-page-box-3-meta-box-id', __( 'Home Page Box 3', 'THEMESLUG_text_domain' ), 'THEMESLUG_home_page_box_3_meta_box_callback' );
  }
}
add_action( 'add_meta_boxes_page', 'THEMESLUG_register_home_page_meta_boxes' );

/**
 * Creates the text box using the WordPress editor for the home page meta box.
 *
 * https://developer.wordpress.org/reference/functions/wp_nonce_field/
 * https://developer.wordpress.org/reference/functions/get_post_meta/
 * https://make.wordpress.org/support/user-manual/content/editors/
 */
function THEMESLUG_home_page_box_1_meta_box_callback( $post ) {
  wp_nonce_field( 'save_THEMESLUG_home_page_box_1_meta_box', 'THEMESLUG_home_page_box_1_meta_box_nonce' );

  $editor_text = get_post_meta( $post->ID, 'home_page_box_1_text', true );
  wp_editor( htmlspecialchars_decode( $editor_text ), 'THEMESLUG_home_page_box_1', $settings = array( 'textarea_name' => 'home-page-box-1' ) );
}

/**
 * Save the text from the editor to the post meta.
 *
 * https://developer.wordpress.org/reference/hooks/save_post/
 * https://developer.wordpress.org/reference/functions/wp_verify_nonce/
 * https://developer.wordpress.org/reference/functions/current_user_can/
 * https://developer.wordpress.org/reference/functions/update_post_meta/
 */
function THEMESLUG_home_page_box_1_save_meta_box( $post_id ) {
  // Check if our nonce is set.
  if ( ! isset( $_POST['THEMESLUG_home_page_box_1_meta_box_nonce'] ) ) {
    return;
  }

  // Verify that the nonce is valid.
  if ( ! wp_verify_nonce( $_POST['THEMESLUG_home_page_box_1_meta_box_nonce'], 'save_THEMESLUG_home_page_box_1_meta_box' ) ) {
    return;
  }

  // If this is an autosave, our form has not been submitted, so we don't want to do anything.
  if ( defined( 'DOING_AUTOSAVE' ) && DOING_AUTOSAVE ) {
    return;
  }

  // Check the user's permissions.
  if ( isset( $_POST['post_type'] ) && 'page' == $_POST['post_type'] ) {
    if ( ! current_user_can( 'edit_page', $post_id ) ) {
      return;
    }
  } else {
    if ( ! current_user_can( 'edit_post', $post_id ) ) {
      return;
    }
  }

  // Save the text
  $editor_data = htmlspecialchars( $_POST['home-page-box-1'] );
  update_post_meta( $post_id, 'home_page_box_1_text', $editor_data );
}
add_action( 'save_post', 'THEMESLUG_home_page_box_1_save_meta_box' );

/**
 * Creates the text box using the WordPress editor for the home page meta box.
 *
 * https://developer.wordpress.org/reference/functions/wp_nonce_field/
 * https://developer.wordpress.org/reference/functions/get_post_meta/
 * https://make.wordpress.org/support/user-manual/content/editors/
 */
function THEMESLUG_home_page_box_2_meta_box_callback( $post ) {
  wp_nonce_field( 'save_THEMESLUG_home_page_box_2_meta_box', 'THEMESLUG_home_page_box_2_meta_box_nonce' );

  $editor_text = get_post_meta( $post->ID, 'home_page_box_2_text', true );
  wp_editor( htmlspecialchars_decode( $editor_text ), 'THEMESLUG_home_page_box_2', $settings = array( 'textarea_name' => 'home-page-box-2' ) );
}

/**
 * Save the text from the editor to the post meta.
 *
 * https://developer.wordpress.org/reference/hooks/save_post/
 * https://developer.wordpress.org/reference/functions/wp_verify_nonce/
 * https://developer.wordpress.org/reference/functions/current_user_can/
 * https://developer.wordpress.org/reference/functions/update_post_meta/
 */
function THEMESLUG_home_page_box_2_save_meta_box( $post_id ) {
  // Check if our nonce is set.
  if ( ! isset( $_POST['THEMESLUG_home_page_box_2_meta_box_nonce'] ) ) {
    return;
  }

  // Verify that the nonce is valid.
  if ( ! wp_verify_nonce( $_POST['THEMESLUG_home_page_box_2_meta_box_nonce'], 'save_THEMESLUG_home_page_box_2_meta_box' ) ) {
    return;
  }

  // If this is an autosave, our form has not been submitted, so we don't want to do anything.
  if ( defined( 'DOING_AUTOSAVE' ) && DOING_AUTOSAVE ) {
    return;
  }

  // Check the user's permissions.
  if ( isset( $_POST['post_type'] ) && 'page' == $_POST['post_type'] ) {
    if ( ! current_user_can( 'edit_page', $post_id ) ) {
      return;
    }
  } else {
    if ( ! current_user_can( 'edit_post', $post_id ) ) {
      return;
    }
  }

  // Save the text
  $editor_data = htmlspecialchars( $_POST['home-page-box-2'] );
  update_post_meta( $post_id, 'home_page_box_2_text', $editor_data );
}
add_action( 'save_post', 'THEMESLUG_home_page_box_2_save_meta_box' );

/**
 * Creates the text box using the WordPress editor for the home page meta box.
 *
 * https://developer.wordpress.org/reference/functions/wp_nonce_field/
 * https://developer.wordpress.org/reference/functions/get_post_meta/
 * https://make.wordpress.org/support/user-manual/content/editors/
 */
function THEMESLUG_home_page_box_3_meta_box_callback( $post ) {
  wp_nonce_field( 'save_THEMESLUG_home_page_box_3_meta_box', 'THEMESLUG_home_page_box_3_meta_box_nonce' );

  $editor_text = get_post_meta( $post->ID, 'home_page_box_3_text', true );
  wp_editor( htmlspecialchars_decode( $editor_text ), 'THEMESLUG_home_page_box_3', $settings = array( 'textarea_name' => 'home-page-box-3' ) );
}

/**
 * Save the text from the editor to the post meta.
 *
 * https://developer.wordpress.org/reference/hooks/save_post/
 * https://developer.wordpress.org/reference/functions/wp_verify_nonce/
 * https://developer.wordpress.org/reference/functions/current_user_can/
 * https://developer.wordpress.org/reference/functions/update_post_meta/
 */
function THEMESLUG_home_page_box_3_save_meta_box( $post_id ) {
  // Check if our nonce is set.
  if ( ! isset( $_POST['THEMESLUG_home_page_box_3_meta_box_nonce'] ) ) {
    return;
  }

  // Verify that the nonce is valid.
  if ( ! wp_verify_nonce( $_POST['THEMESLUG_home_page_box_3_meta_box_nonce'], 'save_THEMESLUG_home_page_box_3_meta_box' ) ) {
    return;
  }

  // If this is an autosave, our form has not been submitted, so we don't want to do anything.
  if ( defined( 'DOING_AUTOSAVE' ) && DOING_AUTOSAVE ) {
    return;
  }

  // Check the user's permissions.
  if ( isset( $_POST['post_type'] ) && 'page' == $_POST['post_type'] ) {
    if ( ! current_user_can( 'edit_page', $post_id ) ) {
      return;
    }
  } else {
    if ( ! current_user_can( 'edit_post', $post_id ) ) {
      return;
    }
  }

  // Save the text
  $editor_data = htmlspecialchars( $_POST['home-page-box-3'] );
  update_post_meta( $post_id, 'home_page_box_3_text', $editor_data );
}
add_action( 'save_post', 'THEMESLUG_home_page_box_3_save_meta_box' );

?>