This is maybe the largest scene you have ever made, in terms of details and number of objects. So we will take some time to learn how to organize ourselves in order to have a more manageable scene.
One interesting thing that Blender has to offer is the grouping tool. Let's see how it is working:
We will group objects that have a logical relationship between them. So we first select every part of the house, such as the foundations, the walls, the curtains, and the fireplace, and we will place them in a group by pressing Ctrl + G.
If we look at the last tool options in the left 3D view panel, we can enter a name for our newly created group.
Now we can select barriers and create a new group with them.
We'll leave the cliff alone, so we don't have to put it in a group.
The rocks will also be part of a group.
We will also group all the cart pieces.