Wow…
Listen, you’re trying to jump into the deep end of the wrong pool with this post. This whole forum is to help people with the Unreal Engine. It’s not a general programming forum that’s going to help you build an engine from scratch.
Making a game engine is incredibly difficult. This is why the usual advice for beginners is to make games, not an engine. First it produces faster results because you’re focused on the outcome of a specific game and not all the supporting things that are hidden. And using an Engine like Unreal, Unity, Godot, etc allow you to shortcut a whole lot of stuff that can be down right tedious.
Unless you’ve been programming since you were 5, you probably don’t have the experience to do this sort of thing yet, even with the best help.
Right now you should be focused on learning. That could be an Engine like Unreal, pure programming languages like python or C++ or quasi frameworks like pygame.
Come up with way simpler games, and then simplify some more.
Everyone has their dream game they want to build, but you need the foundations first. Write down the details of all the things you want it to do so that you can come back to it later when you have the skills. Take parts like managing an inventory and do that as a separate project where you can practice building just that without worrying about anything else.
If you want to practice doing that sort of thing in Unreal, this is a great community that can help you accomplish those things. If you want to do it entirely from scratch, find and reach out to the myriad of developer communities on the Internet that will help you with your goals.
Best of luck to you!