Template for individual post designs

This shouldn’t be very difficult.

WPs Template Hierarchy should get you started on what page loads every time.

You’ll probably be best maintaining minimal header.php and footer.php and working your logic on single files, named as per the Hierarchy.

Then, head to add_meta_box() and update_post_meta() to implement those selectors for css and js and also any switches to toggle.

Then, it’s about the best use you can make of the Conditional Tags to dinamically find out which content you’re loading and fetch the right files for it.