Action RPG Inventory System

What you are talking about is simply the UI layout and that has nothing to do with an inventory system, items or game mechanics.

An Action RPG is a very broad genre.
For example Skyrim/Fallout 4 are action rpgs because they have a strong emphasis on combat.
You could switch this Demo UI to be a Fallout/Skyrim item list, or a Jigsaw grid layout like Diablo, or a position in a bag layout like oldschool Darkfall/Ultima Online with almost entirely only making UMG UI changes.

But that is assuming the person has some level of knowledge in UE4 and development.

It should be pretty straight forward for people with some experience blueprinting in Unreal.
I will be creating a tutorial series after the launch of the TopDown Kit to show how to integrate the two.