Christine,
A suggestion for you to consider. If any of those old windows that were in the barn are salvageable why not frame in the upper area and put them in there? That way you would have some natural light coming in from above, plus if they are double hung sashes you could open them in the summer and put screens in for added ventilation.
I hope you are saving the old siding and resuse some of it to save on costs of materials. You can probably use it for some of the rough in work or even with some trimming reuse it for actual siding.