This is so awesome! Every time you create a plugin it seems like one I've needed. My game is heavily inspired by Stardew Valley with a mix of Pokemon (capturing monsters) to fight in ABS style.
I made myself a hotbar UI with eventing but it's kind of messy and causes lag so I'm exciting to use this when I get back to working on my game after taking a holiday break.
One quick question: Does this allow the user to stack items? In Stardew Valley, the player could have stacked items in the bar and the number of items the player has will show up in the box. So if a player plants a seed, the number will go down so they can see how many seeds they have from the hotbar.