That is beauty of doing game dev, there are no tutorials! I hope you are doing it for challenge and because you love solving complex problems.
And all you seen done in other games is possible with unreal, but usually not easy\simple\fast to do.
Most things have no tutorials or button “make my game”.
Best advice here: split your tasks\problems into smaller problems. Then split those smalle problems int oeven smaller ones. And keep splitting until you cannot split them anymore. Then code it all from simplest things up to your whole open world game.
For eg. AI drive a car problem: (how i would split it into smaller things):
- learn how AI is done in unreal
- make car driven by player, learn how to do it. Decide if i need physics car or just simple car.
- it does not matter if character AI drives car, or car drives self with some dummy character inside
- learn how to posses/unposses things in unreal
- make player steal car by possesing one and replacing npc dummy character with player dummy.
You need to split your whole game into smallest pieces like that.
But i strongly suggest you make very simple game first, going open world GTA style game as your first game will get you burned. Just google how many man hours took to make gta.
Do something tiny first, like racing game on track (and do not touch multiplayer until your 5th or so game.).