1. You should edit theme files to add email button.
Please edit /wp-content/themes/citytours/single-hotel.php file and /wp-content/themes/citytours/single-tour.php file to add "Book by email" button.
2. I can not understand what you want.
3. You can not delete tour price in citytours theme.
4. You can not add the other information to checkout page.