Hi Alan,
Yes you can use a plugin to insert ads on the home page.
For example https://wordpress.org/plugins/ad-inserter/
You ca set the number of posts it shows on each load by editing the jetpack.php file located in /inc/ folder of your theme.
Replace the contents in the jetpack.php with the following code
function novapress_jetpack_setup() {
add_theme_support( 'infinite-scroll', array(
'container' => 'main',
'footer' => 'page',
'type' => 'scroll',
'posts_per_page' => '12',
'footer_widgets' => false,
) );
}
add_action( 'after_setup_theme', 'novapress_jetpack_setup' );
Change the posts_per_page value to what you want.
We will be releasing an update for Novapress Pro soon which will allow you to set this number in the Customizer.