Hello,
1) Not sure about this. You may try third-party plugins to add the Ajax add to cart for the variable products https://wordpress.org/plugins/woocommerce-ajax-add-to-cart-for-variable-products/ or https://wordpress.org/plugins/woo-ajax-add-to-cart/
3) Copy function http://prntscr.com/ul53z3 and add the font you need to the list of available fonts.
If you need to change any functions or add hooks you can use child theme functions.php if anything else is not mentioned in the plugin docs.
4) Just paste the svg code there http://prntscr.com/ul586q
Regards