First things first:
What genre of game are you making?
Is it platformer, RPG, infinite runner etc?
Platform games can be made all in one layout using layers or by random placing platforms and enemies.
RPG can also be made all on the same layout using different layers and random placing of enemies, objects, friendlies and obstacles.
I rarely use more than 3 layouts in any game I make and one of those is a menu and one is for storage of items for inventory or maybe a special scene like transferring from outside to an inside perspective.