Maximum number of posts per page before affecting performance?

You need a js file..

Then call using js a stream

function ajaxStreamCall(){
    $.ajax({
            type:'POST',
        data : {
            action: 'get_stream',
            offset : +++ //you will need to find a method to offset from your current posts
        },

        success: function(obj){
            $(obj).prependTo('#news-stream');

        },
        url: "/wp-admin/admin-ajax.php"
    });
}

You will need to find what your offset is, maybe just count your current stream (posts) and tell it to offset that many..

BTW.. If you are lost already, just find a plugin to do this, im not giving 100% how to, you will need some WordPress / Ajax knowledge

Next in functions

add_action( 'wp_ajax_get_stream', 'stream' );
add_action( 'wp_ajax_nopriv_get_stream', 'stream' );
function stream(){
  $post_offset = $_POST['offset'];
$args = array( 'numberposts' => '10','offset' =>$post_offset );
$recent_posts = wp_get_recent_posts( $args );
foreach( $recent_posts as $recent ){
        printf( '<li><a href="https://wordpress.stackexchange.com/questions/253363/%1$s">%2$s</a></li>',
             esc_url( get_permalink( $recent['ID'] ) ),
             apply_filters( 'the_title', $recent['post_title'], $recent['ID'] )
         );
    }
}

Now just use jQuery to append this to the end. Again.. This is just an idea of how to do this. If you have questions let me know. Hopefully this sets you in the right direction.

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