There are two techniques that can be applied here. Initially I left the characters layer as 2D. The pros is that it is simple in the placement, not having to mask any thing if the characters intersect with the 3D objects in the room. The downside is it does not look as integrated into the scene and looks flat. Thus, I decided to change the layer to a 3D object. Depth of field can also be achieved better.
The background assets were crafted in Illustrator and Photoshop. Some of the textures I had found online and used the image trace to create a simplified texture graphic style. The rest of the objects and furniture such as the plant pot and picture frames were done in Photoshop.
I have a number of environmental scenes that needs to be constructed before I begin rendering the shots and importing it into Animate CC to do the character animations. Within each environmental scene of ground, building, sky textures, there will be other assets such as furniture, cars, benches etc.