Now that the three walls are up on the basic shell, there is nothing else you can do to it until you get the staircase done.
The instructions are not very helpful for building this staircase. I put it together from experience of how dye cut staircases go and the one sorry looking picture in the instructions which is so dark and without detail that the only thing you can get out of it is the direction the staircase is suppose to wind in.
The railing of this staircase are solid pieces which look like walls but they are not. The handrails go over them. This is useful info because you might think that the railings are suppose to make a stairwell and you can get tempted to wallpaper them.
I am going to stain the staircase to match the floors so I can assemble it in its entirety. If you plan on making a two tone staircase then you will have to paint each individual part separately and then assemble it.
Look at the pictures of my staircase carefully. I purposely left out the risers and steps so you can see how it's put together. I took pictures from all angles so you can see how each part fits. It's extremely complicated to say the least. The stringers will give you the most hassle because it's hard to make out how they go exactly. Notice how the tabs go under the cross section of the staircase at the bottom and the back wall holds them in place. You must glue a stringer to the staircase wall, then the back wall and then the last stringer.
You must keep the tabs in mind so you don't apply any part flush to them, covering them up by accident. Double check your work often and don't glue anything in place until you're 100% sure that you have it right.
Don't try to dry fit your staircase in place in the dollhouse. If you try to dry fit it before you staircase assembly is completely dry, you will pull it apart from the pressure. Let it dry very well. Believe me, you do not want parts to begin falling off and then you have to struggle again to find what goes where.
I tried to see if there was a way to build the staircase while in the dollhouse so I wouldn't have to try and fit the entire assembly in at once but there isn't. It must be assembled away from the dollhouse in it's entirety.
Make sure you also finish your staircase completely before putting it in place.