Customize existing wordpress plugin or create new one for Build Your Own Snackbox project

We are a start-up company looking to create an ordering service for custom snack boxes (Build your own snackbox) using Wordpress/ Woocommerce. Basically the customer will have the possibility to choose the box size and what items he wants in his box. I tried the extension Composite Products from Woocommerce and it does almost what we need. However, I would like to have the possibility to have only one step and the user will be able to add more than 1 product. In Composite Products each component only allows one product to be selected so for example if I have a box of 30 items I must create 30 steps and looks messy. Please have a look at this example (click on demo) [login to view URL] apart from this problem, I think will be ok with the right modification. I also tried Mix ‘n Match extension but the problem with this one is I will have about 400 products and doesn’t have the filters and sorting options so will be very difficult for the customer to find the products that he wants to add in his box. The ordering process for the customer: Customer selects the preferred Box size (which is like a main product), for example: Build Your 10 Snacks Snackbox then the next step is: Choose your Snacks – here the customer will have the possibility to add 10 items and filter them by allergens, category or something else and sort them because I will have about 400. In this products list he will see the title and a button add to box but if he will click on the title or product image he will be able to see title, description, nutritional information and allergens of the product(as a pop-up or product page) On the right side will be “Your configuration” which is a list with the products in the box and how many must be added to fill the box and then a button add to cart (like in Composite Products example) Once they filled the box a button or a pop-up should show and offer them an upgrade to a bigger one (if it’s available) For example: They filled the 10 product box they will be asked “Do you want to upgrade to the higher box for the difference of £3?” We don’t need stock management for any of these products. On the admin side I want to be able to create as many boxes as I want with title, picture, description, how many items are allowed to be added, price/ discounted price and select the products category that items are allowed to be added into the box. For example: Small Snackbox, Price is £12, description: Add your favourite 10 snacks, products that can be added: from specified categories or items Another example can be this website [login to view URL] the workflow it’s similar and we like this. If link is not allowed please let me know and I will remove it asap. To be honest I think will be better if we can modify the plugin Composite Products as I believe it does almost what we need and the customisation will be faster.