I want to start the process of dumping my ideas into a game engine, but I'm unsure of the best order to do this.

The way I see it is I've got two options:

1: Make all the pretty landscapes and models and add all the code in later.
2: Start off with a basic room with place holders and add as many features as I can before adding in the proper landscape and models.

Does it matter? Would I run into problems doing one way instead of the other?

I should probably just dive in and do it but I have this horrible fault in me where I have to double check every damn thing before I try something lol