Hello Itorius,
Do you plan to have the inventory be something like a grid-like system? Will there be a max amount of slots and what determines when these slots are created?
The easiest way to do this (depending on your existing knowledge) would be to use an array to store the entire inventory. The inventory array can either be an array of references to blueprints/classes based off a “Master” class that all inventory items inherit from or an array of inventory slots.
After you have the array, you can have the Widget base its slots off this array. If you wish, the slots could always technically exist but just never be visible unless that slot is populated in the array.
If you need more specific details on this, let me know, but this is a general overview of just one way to do this.