So in short: From my experience, only work with massive layout sizes if you are using small and few textures within that layout. Construct seems to want to draw EVERYTHING in a layout at load-up, so creating a whole world in one layout is bound to be problematic.
Construct Classic probably loads all graphics into RAM if an object exists in the layout to avoid predicting when to load and free the RAM. Only a custom engine can probably get away with that because they are designed for a specific game.
The trick is to load certain parts of the game near the player at runtime, and free up memory of things far away like SoldjahBoy said. Only position/angle/status data needs to be stored of an object if it loads a texture/model from a file, otherwise you should be able to store the custom or modified texture to a file and load it again later.