Thanks for #1. That was what I needed to make it work.
For #2, I inserted my COUPON CODE that I created with minimum quantity 10 into ‘COUPON_CODE_HERE’. I also changed it to $amount = 20 * floor( $amount / $min_matching_product_qty );
This makes more sense and gives me the result I want since if min quantity is set as 10 and I order place 10 in cart, that will return a 1 multiply by 20 and that amount is added to cart for free. For 15 it returns 1 as well and for 20 it returns 2 which gives me the desired result.
Let me know if my logic is off and if it will create problems. Thanks!