WordPress provides a filter called wpmu_new_blog and passes the parameter $blog_id (the ID of the new blog) and $user_id (the user, that just created that new blog) (and some more) to it. You can hook into this action to create the new pages and edit the options:
<?php
/**
* Plugin Name: Default Site Structure
* Description: Crates default pages and set them as front/blog index pages.
* Network: true
* Plugin URL: http://wordpress.stackexchange.com/a/219504/31323
* License: MIT
* Version: 1.0.0-alpha
*/
namespace WPSE177819;
add_action( 'wp_loaded', __NAMESPACE__ . '\init' );
/**
* @wp-hook wp_loaded
*/
function init() {
add_action(
'wpmu_new_blog',
function( $blog_id, $user_id ) {
switch_to_blog( $blog_id );
$front_page_id = wp_insert_post( front_page_data( $user_id ) );
$index_page_id = wp_insert_post( index_page_data( $user_id ) );
if ( ! is_wp_error( $front_page_id ) && 0 !== $front_page_id ) {
update_option( 'show_on_front', 'page' );
update_option( 'page_on_front', $front_page_id );
}
if ( ! is_wp_error( $index_page_id ) && 0 !== $index_page_id ) {
update_option( 'page_for_posts', $index_page_id );
}
update_option( 'date_format', date_format() );
update_option( 'time_format', time_format() );
restore_current_blog();
},
10,
2
);
}
/**
* Returns the data of the blog index page
*
* @param int $post_author
*
* @return array
*/
function index_page_data( $post_author ) {
return [
'post_title' => 'My blog index',
'post_content' => '',
'post_type' => 'page',
'post_author' => $post_author,
'post_status' => 'publish'
];
}
/**
* Returns the data of the front page
*
* @param int $post_author
*
* @return array
*/
function front_page_data( $post_author ) {
return [
'post_title' => 'Hello World',
'post_content' => 'Welcome to my new site!',
'post_type' => 'page',
'post_author' => $post_author,
'post_status' => 'publish'
];
}
/**
* Returns the custom date format
*
* @return string
*/
function date_format() {
return 'd,m,Y';
}
/**
* Returns the custom time format
*
* @return string
*/
function time_format() {
return 'H/i/s';
}
Use this plugin as mu-plugin and it will affect each new blog. This example edits all option keys directly. You should take some time to figure out, whether WordPress provides API functions to setup these options. (Something like wp_set_front_page()…)