Java | Woocormerce API developer

I have a simple JAVA swing project which talks with woocommerce API and displays
the woocommerce products from my website. The application is almost done but few things I
need to work on are below:

All I need to get done is when I press
a product and if it does exist product variations and options like size S,M,L,XL etc
then it needs to show it, if do not exist then do not show it.

For example: I have a Pizza in one of the products with it's sizes and toppings
Now when I click on that pizza product then show the size and when customer click
the size and if the pizza has toppings then give them the option to choose the topping
display the price accordingly in product name and price panel (make sure we are using woocommerce API)

Finally, integrate the payment method into the application using woo API so customer can pay on the POS.
And if other problem exists, I want to work long term with you if I get satisfaction on the work.