Due to the small size of this dollhouse, I recommend assembling the window bays completely away from the dollhouse. Completing the interiors will be very difficult otherwise. The bays are detailed and feature large windows, but they have limited wall space. You might consider finishing them in a different style instead of using wallpaper. I plan to stain mine to match the interior trim.
The bays also include window seats, which you may want to upholster. I plan to do that after finishing the dollhouse. For now, I have assembled my bays and will let them dry. Once I complete the interior of the dollhouse, I will continue working on them.
Although the instructions suggest adding window trims at this stage, it’s best to wait until after you finish the walls to do so.