From all the experience from making things like SCPF sites ranging to survival games from my point of view scripting should be the first part of any project, I’ll explain why.
When making a game you want to have its core features to be on point otherwise players may call your game broken which will not attract more players to it, thus meaning you won’t profit.
Survival games like this should focus on core mechanics on things like guns and inventories because later in development some problems may arise.
Personally when I made a survival game and did the backpack system the last I had to redo every item there was ingame because my code just couldn’t work with the objects I made already ranging from not just being able to pick up the item to the item just disappearing for no reason from the game.
This is overall my view on how you should start your game but sometimes building first might be a good option to then be able to think how you’ll code the game.