Hi,
This is really going to depend on your skill level with PHP and experience with WP dev.
Ideally, you would want to work with a dev if this is not something you are overly experienced with.
1) Yes, this can be added to a child theme. I missed that filter initially. In your child theme functions.php you would use this:
function pb_product_pages( ) {
$pt_array = array('page', 'post', 'portfolio', 'product', 'team', 'jobs', 'ajde_events');
return $pt_array;
}
add_filter( 'spb_pt_array', 'pb_product_pages' );
2) It would be complex to do this in a child theme. You could look to remove the filter add_filter( 'rwmb_meta_boxes', 'sf_register_meta_boxes' );, create your own new function in the child theme sf_register_meta_boxes_child() and then add that filter: add_filter( 'rwmb_meta_boxes', 'sf_register_meta_boxes_child' );.
3) You can just duplicate page.php and then add your own template name at the top of the code:
<?php
/*
Custom TemplateFull Width Page
*/
?>
.