Hey Cypaubr! I actually did a top down shooter in UE4 about a year ago, just as a small side project. You can see some of my early results here.
Besides from the inventory system, I did everything from scratch, starting from the base top down example project included with Unreal. The biggest resource I used was this website, Shooter Tutorial.
While the website shows how to create a shooter game from just a first person view, it still goes over a lot of important things, like how to setup your guns, and more. For animations I used a free pack off the marketplace and then a couple custom ones.
Honestly a place I would begin with is an inventory system. This system will drive quite a lot, even your weapons (eg weapon can extend from an item class).
I can’t remember exactly where I found this flowchart from, but I still have it saved, but its essentially the same way my classes were setup (at least for weapons).
If you have more questions, feel free to ask!