I think it’s very doable, since UE4 comes from originally an FPS background. And as a LAN-only game the multiplayer would be much easier to set up. Though understand, that even with things like Blueprints which can help make things easier, there’s still a lot to try and learn, and if you have coding experience then they make sense as far as what they do and what they make easier vs. doing coding. But you’re still going to have to learn some of the things that you would need to know for coding.
However, I don’t know that the idea is all that compelling, for one as a LAN-only game I think many people wouldn’t be interested in playing. And as an FPS there doesn’t seem to be any features that would draw people to want to play it, like what makes it different from other FPS games?